Defense Grid 2

My advice to get this would just be to sell towers as you finish a level (if you remember.)
If you really need to go for just this achievement, you could do the Tutorial, fill every spot with guns, and then sell 10 of them.

As with all other achievements in this game, this will not unlock until you beat the level.

*Key note the achievement will not pop until the end of the level so don’t worry if it doesn’t appear straight away*

In this game you can easily pick up 15 achievements in the first 2 levels for this particular achievement all you need to do is load up the second level and half way through the level you should have about 500 resources spare and also a good set up which will take all of the aliens out for you. Find a spare few blocks that allow you to build and build 5 towers them sell them straight away repeat this again and you will have sold 10 towers it does mean you will lose 500 resources but you should be able to play without them

But you can also pick up another 14 achievements at the same time

First Blood: build one gun tower at the start of any level once the enemy spawn you will unlock this straight away as there is no way you can do this without killing anything.

2 YELLOW BEATS GREEN: at the start of the level when you build your first turret click it with A and choose to upgrade it and this next achievement will unlock for you.

CONFIDENT: Once you have placed 5 or 6 turrets onto the field click RB on your controller so the game speeds up and as long as you have enough turrets on the field you can leave this on all game so you can be certain this achievement unlocks for you.

SURPLUS: while playing the level you will notice a bar with all the enemies you have left to kill when you kill the last set of enemies quickly sell as many towers as you can so that it takes you over the 1000 resources as long as you sell 2 red towers you should be fine.

THANKS FOR PLAYING: when the game starts if you set up 5 or 6 gun turrets and upgrade them to red status it will stop any aliens getting through which will mean at the end of the level you will get a silver medal and another achievement popping

FIELD PROMOTION: same as above.

ERADICATOR: you will naturally pick this up in the second level just by playing the level a few minutes into the level you should pop this achievement it is almost unmissable.

INDECISIVE: Same as the current achievement

ARSENAL: if you do the achievement above you should have already built 10 towers but you should naturally already have 10 towers built to stop the aliens already which will allow you to unlock this achievement if not build a few more gun towers and the achievement is yours

HEY THATS MINE: for this one you need to let an alien get to your power ores and then kill them but I would recommend watching the video guide I have included below and it will show you how to get this and the other two achievements below, you should naturally pick this up at some point but if your specifically going for it let the aliens run through without building any towers once they are at the end start building towers to kill them

HAPPY RETURNS for this achievement you have to kill an alien who has took one of your cores and then let the core get back to the base without any more enemies stealing it

CLOSE CALL for this you need to kill an enemy who is about to capture your core and is 10 seconds away from it being fully stolen, you need to then kill that enemy and help the core get back to base to unlock this one but again if you watch the guide below It will show you the set up I used

DEATH FROM ABOVE: if you choose the officer at the start before the level loads press and hold the right trigger until the laser fires it doesn’t have to be over an enemy to get the achievement but I would recommend it to help you with the level

RETRY at any point of any level just click LB and it will take you back to the start of the last enemy who came to attack you. I would try to be wary of this button though as I have often clicked it by accident and had to redo a level I had already done easily.

I have also included a video below on how to unlock all of the achievement I have talked about in this guide and talked through them all if that is more helpful for you.

Pretty self explanatory from the description. Here's how to sell towers:

Press with the cursor over the tower you want to sell.
Move to the option "Sell Tower: xxx"
Press to sell

Best to do this in a later stage, maybe start out with some weaker gun towers and sell them at some point through the game to make room for more powerful towers.