I'm assuming "the other one" is the RC3 update? Do this:

Have a file manager window open to the folder with that RC3 update zip in it. Right click your desktop and go Litestep >> Quit. Another file manager window should open to the Litestep folder. Extract the RC3's zip's contents in to that folder with the litestep.exe in it, allowing files to be overwritten. Double click litestep.exe to restart Litestep.