My competitors actually sell $8 kits! But it's free when you do it yourself! It only takes a minute.
Here are three pictures that illustrate the DIY process. Make sure you unload the mag first. And don't make a 50 rounder if they are not legal in your state.
The spring doesn't need to be attached to the floor plate for mag to function normally. This 1 minute mod doesn't include an attachment point for the spring. Having the floor plate attached to the spring is handy because you are less likely to lose that small part during a mag disassembly in field conditions. If you are worried about losing the floor plate during magazine field strips, this is where the super glue comes in. Just glue the top and bottom parts of the plug together.