I accidentally changed my build to 4.6.1f1 and now i dont know who to change back?

im a complete noob when it comes to unity. im just trying to script a few things in uscript for my assignment for university, problem is i pressed the build button without knowing what it doesnt and now im on unity 4.6.1f1, i don't know why how or what this is but i just want to get back to 4.6.1, preferably without losing my work, so that i can script it again, because uscript says it wont work with this new build iv created, im not looking for an explanation of what iv done, i just want to go back :(,