Yestarday i purchased a macbook pro from dezembre of 2011, all seems to work fine like all macs but there is several issues concerning me. It happens that it brought no system dvd and there is this user web page where the guy has more then 13gb in any visible file, its a lot of space so with this i downloaded houdini to see what files were hidden and it happens again that i can't erase none and also there is no directory with such a value of gb in it. What can i do to erase this disk space? Should i buy the new system of mountain lion and try to erase everything? Or is it easy to format and install a new system on mac?