As Henry Carter says its easy enough. I suppose it is easier to do these things with confidence if you have done a bit of sewing and alterations and watched others doing it. Most libraries have millions of modern books with illustrations and DVDs on anything you want to do in sewing, tailoring and alterations.
Just get an unpicking tool, everyone should have one anyway. Carefully unpick/cut each stitch then patch will be off.
The unpicker is safer than scissors.