Buy the 13 rounders.
Trying to make the 10 round magazine to a 13 round magazine, will compromise the integrity of the magazine.
If you dissassemble your 10 round magazine and look down the magazine body, you'll see side rails which constrict the round capacity to 10.
You could dremel out the side rails, but you would have to cut through the metal liner and the polymer magazine walls. This will severily compromise the reliablility of the magazine.
Way easier to just buy the hi-cap magazines, they are still cheap (under $20).