Tony Hawk's Pro Skater 1 + 2

From the main menu select "Skate Tours" and choose Tony Hawk's Pro Skater 1. Simply play through the levels, completing as many level goals as you can, as well as earning medals in the competition levels.

Once you complete enough goals (I think it's 51 in total) you will unlock the Roswell level.

If you go down to the Roswell level in the Level Select menu it will tell you how many goals you need to complete to unlock it.

If your achievement has bugged delete your save from the console(NOT FROM EVERYWHERE). Once this happens go offline and start-up Tony Hawk. If the game takes you to the Terms and Conditions page where you have to scroll down then you have been successful so far. Make sure by now you have reconnected to the internet. All you have to do now is speed run the entire Tony Hawk Pro Skater 1 tour. You need to reunlock enough goals and as soon as you unlock Roswell you're achievement will pop. Do not worry about your old account getting lost. Once you're done quit the game and delete this save from the console. When you reboot the game your old account with the highest progress will load up. I hope this helps those who have bugged out from it. I tested it on my account with success.