When grip bushings are staked, the back edge of the bushing hole is slightly beveled. When the bushing is staked, it expands into the beveled area. The bushing can't extend into the magwell or it will cause the magazine to hang up.
Get the tool from Brownells, its good to have. Its very easy to screw up the slot in the bushing. If it seems really tough to get out the bushing, you might first try putting some heat on the bushing in case its held in with locktite. If that doesn't do it, them its probably staked.
I have only run into staked bushings once, and it was just last week on a Springfield Mil Spec that had been converted to an accurized Bullseye wad gun by George Madore. Now maybe George Madore had staked the bushings, and not Springfield....I have no way of knowing.