When you open Sked+ click the Open Time tab that is at the very top. It will then show you your schedule with all the reserve days on it, etc. Click on the colored bar during the day of duty you want to move. It will pop open a screen that says reserve details. Click the exchange link and it will take you to another screen where you can select the day you want "exchange". Check the day you want to move (using it tonight it only allows you to select the day either at the beginning or the end of the block of reserve days) and then there is a small field on the right where you can find through a calendar the day of reserve you now want to work (in other words select the off day you want to move here). Click Next and then it will ask you for your password, put that in and click submit and it sends it into the queue where it should be processed within 60 seconds after it checks legality.

Hopefully that makes sense, pm me if you still don't understand