Still didin't work.
Can you do it for me?
Best way to learn is to do it yourself
First open your gif/video and then goto filters

Then add the resize filter


Then configure the filter (Below settings are for a forums avatar) and hit OK

Then goto cropping

Adjust the edges to your liking and hit OK

Then export your finished video



You can also remove frames by marking a section in the seekbar using your Home (Selection start point) End (Selection end point) and Delete keys.