Hi Mary Lou,
If I recall correctly, this is sometimes caused by a minor misalignment of the fields for the two address line fields.
Press shift-command-L to enter Layout mode, and align the left edges of lines 2 and 2 of the label layout.
Another factor may be that lower lines will move up only if the unused line is "empty." If line 2 is a Calculation field, the calculation may be inserting one or more non-visible characters, resulting in the field appearing 'empty' while actually containing one or more characters.
Barry, thanks for your suggestions. My delay in replying comes from an unexpected trip to the hospital to get my gall bladder removed! I'm home and feeling quite good.
I tried your suggestions but couldn't get rid of the third line from the address labels that only needed 3 lines.
I'll keep fooling around.