Are you using a green apple loop or a blue one? Either way, all you need to do is click on the region you want to change, then go to the region parameter box (directly above the channel strip on the arrange page). There you will find Transposition as one of the editable parameters. If you click on the double arrows, you can change the octave, and if you click in the blank space next to the word "transition" you can move in increments of half steps. You can split a loop with your scissors tool, then apply different transition values to each part of the loop if you want your change to happen mid-loop.
In a green apple loop, you can also open it in the piano roll editor and select the notes and move them anywhere on the grid you want, and even change notes around to alter the the melody if you feel the need.