For starters, go into layout mode and check out Format | Set Sliding/Printing....
You can set fields to slide up and shrink when they are empty or contain fewer lines of data than the field height you have set in the layout. They can't grow and the change is only visible when you preview or print the report. It can be a bit quirky, as you have several options and have to be a bit careful not to overlap fields, but it can be made to work.
Check that option out and if you have questions about it, post back to the forum and we'll help you out.