In the piano roll, in between the delete and select tool, there is a cut tool which allows you to cut the notes in half.

Also, for a more precise editing, all you do is double click on a note and then you can set the note length and start time and stuff

for extended patterns, you might want to select using the select tool, and copy paste the selection so it doesn't become tedious having to edit every single note

Also in the top right of the fruity toolbar there is a 'SNAP' setting and it is usually set to 'line'. Change that to 1/2, 1/4 or None, depending on how short you want the notes. Then you should be able to shorten the notes to your liking.

thank you so much guys... it helps so much

A great way of doing drum rolls is to select the 'snap' to 1/4 or whatever is appropriate.. then draw a nice long note and highlight it. Select tools->Quick Chop....

You now have a nice long drum roll. Change the velocity of the notes in the piano roll... to easy