While revert means to return to something earlier or to go back, it's often used wrongly in combination. If you're buying the older version of the game, you might say you're "reverting back," which is like saying "go back back."
Revert has been around since the early 14th century, and it has changed little in meaning from the original "turn back" and "return." You can revert to a simpler way of life or revert to bad behavior. Software users might revert to an older version of a program with fewer bugs. Though rare in modern use, some international English speakers do use "revert back" for "reply" in writing and e-mail, but most of the time, using revert with "back" is redundant, or repetitive.