Pruning a Japanese Snowbell!!

I have a Japanese Snowbell--about 5 ft. and was wondering when would be the best time to prune. I am a novice gardener--so I think the bottom should be somewhat smaller than the rest--is this in fact true? Thanks for any help!!

 

If in doubt, don't. You can always cut more later. You can't put back what you cut off.

 

Thanks Ron--I will leave I think!!