Gosh! I did this last week and I can't remember
but click around until you find the "Custom" option - then follow your nose from there. You'll have to delete any current partitions and create everything else you need. Just don't click on the "write/save" option until you are satisfied. I was in the same positon as you once but I'm not there now ----- ie I don't have the screen in front of me (sorry
) !!
Good luck!