Once they are out, just replace them with a button head machine screw. I have forgotten what the thread is on them but the button heads are available SAE or Metric.
The original bolts installed are anti-theft devices. They are soft steel, not hardened and normally the heads can be drilled off with a 5/16" or 3/8" bit.
Drill the head off, separate the top and bottom, use a vise grip to unthread the remaining studs or drill them out entirely and re-thread the housing.
It is rather simple and not difficult to do at all. I've done a few.