It is not very hard job.
1. Screw IN the old studs as far as possible so that their riveted ends come out from the back of the hub.
2. Grind down RIVETED ends with angle grinder or Dremel tool.
3. Screw OUT old studs.
4. Screw in new studs. Or you can use M8x30mm or 35mm bolts but it works only with drum brakes. If you have front disk brake you need to use only studs.