Its quite easy and fast!
Heres what you need:
Obviously, your watch that needs to be resized
A fairly thick needle, preferably one that doesn't break as soon as you pound on it
Something heavy to hammer the needle
Find the little holes in the links of your watch
Make sure your needle fits into the hole, if not pick one that fits
Choose the side with the most links first
Set your needle in the hole of the link you need removed
Gently hammer the needle until the connection comes out the other end
Using pliers, pull the connector out
Do the same for the other connectors until link can be removed
Hope this helps!