You can settle on:
- giving your own dimensions to your animated gif (in this case you write your wanted dimensions on to the step lower).
- decreasing animated gif size and keeping original dimensions.
- giving new dimensions in percentage.

Manual resize Optimization 2 times the original size 3 times the original size 4 times the original size 5 times the original size 6 times the original size 7 times the original size 8 times the original size 9 times the original size 10 times the original size 1/10 of the original size 2/10 of the original size 3/10 of the original size 4/10 of the original size 5/10 of the original size 6/10 of the original size 7/10 of the original size 8/10 of the original size 9/10 of the original size