Plants vs. Zombies Garden Warfare

You rank up character by completing challenges. Pause the game while playing as a character to see what challenges you need to complete. Do the required number of challenges to rank up that character and your player level. Each character goes to level 10. Just rank up any combination of characters 5 times to get this achievement. Rank 1 on each character only has 1 very easy challenge, so this achievement pretty much unlocks from trying out most of the characters for a few minutes.

You get ranks by completing challenges and leveling up characters. Simply level up any characters around 4 times and this achievement should pop. You can see the challenges you need to complete on the pause menu.