Marissa,I believe you are trying to change the stem length. It is quite easy in Finale.
Open the document, and click on the 'special tools' icon. It looks like a hammer and a wrench and a screwdriver. A new toolbar appears. Find the beam angle tool and the stem length tool. Click on the measure and they will allow you to adjust your beams and stems. On the beam angle tool, (if notes are beamed) click on the left box and use the up/down arrow keys to adjust length. The right box changes beam angle. The stem length tool works the same way for notes that are not beamed.
You may also want to use the staff tool and the lyric tool when running into spacing problems. Use the staff tool to increase space between staves in a system and adjust lyrics positioning by using the lyric tool. It gives the document a clean look and the musicians will appreciate it when sight reading.
Robert