There are several ways to reduce the size of recordings.

1. On the Performance tab of the Settings window there are two settings you can adjust:
You can reduce the color depth of the recording.
Reduce screen resolution while performing the recording.

2. On the AVI Video tab, you can reduce the frame rate. However, this will make fast
screen motion look slightly less smooth.

3. If you are not going to use the audio, you can turn off sound recording from
the General tab.

4. Finally, you can convert the AVI file to Windows Media format (WMV). In fact,
My Screen Recorder Pro can do this automatically using the Auto Task feature.
Instructions on using Auto Task are in this article.