If you have 2GB of RAM, that would be enough to download Mavericks.
Does it say your need to free up Disk Space?
If so, you need to remove files from your home folder, like documents, movies, music, photos, etc.
If you don't need them ever again, trash them and empty the Trash.
If you do need them, move them to another location, like an external drive (or two, so you have a backup).
However, I would take the previous advice to buy more RAM as 2GB won't run Mavericks very efficiently.