I am a male so I've never been able to do this (nor would I) but the science behind this would be pretty straight forward.

You just need to make a goal to 'cut' weight... You basically need to do the opposite of what a male body builder would do and you need to trigger catabolism of your muscle to lose them...

As a female you simply do NOT have the testosterone to really grow big... that's in your favor if you want to have smaller muscles.

If you're CERTAIN that this isn't fat... then you can just start having your body burn your muscle for fuel.

1. don't lift the muscle groups that you want to shrink.

2. eat at a protein deficit... don't eat NONE but you should instead eat very little amounts of protein.

3. eat at a caloric deficit. This will cause your body to exhaust fat as a calorie source and go to muscle. It needs to be a SIGNIFICANT deficit below 31 calories per lb of body fat. This is the max your body can burn from fat so if you are more than this you will either pass out from exhaustion or burn it from your muscles.

If you have ever seem someone starting due to famine where they look emaciated - this is what you're going need to do ... don't go to THAT extreme though ... but your muscles will thin out.

Once you hit the right level, resume a regular protein intake along with lifting.

Also, make SURE you do not have a psychological eating disorder... if you have something like body dysmorphia - this would not be good advice to follow.