go to a hardware store or home depot and ask for a strip kit...a strip kit is pretty much special drill bits that you set in each bolt and use with a drill to get the bolts out.....after this i suggest you go and buy some new bolts that fit and use the right size allen key so they dont stripp out again.....this should cost at a max of like $10? just an estimation.... good luck haha
Cut a slit in the head of the allen bolt and unscrew it with a flathead. Next time make sure you use the proper size allen keys, which I assume is the cause. Allen keys should fit nice and snug in the bolt with little to no wobble at all.
^ Try that, but with a Torx wrench. Those are the star-shaped ones with six prongs. You're probably gonna have to just cut the bolt though, strip kits don't like to work on these bolts because they're hardened steel alloy and above grade 8.
dont do what iRIDE NITRO says....it will most likely damage your tools and or make the whole situation worse....i did this once on my bike stem and snapped my allen key in the bolt and was never able to get it out...it could go both ways but i suggest you dont doit.....i definitely suggest what ConnerD said to do....