These wouldn't be right hand threaded bolts would they?
The bolt should be a right hand thread like all of the rest of the bolts.
Right hand = Righty tighty, lefty loosey. Turn the bolt counterclockwise to remove it.
A socket head bolt that uses a 5mm hex wrench should use about 7-8 foot pounds of torque to tighten or loosen it.
For one of those typical bent, hand held wrenches this can be quite a load but for a 3/8" drive socket with a 5mm hex bit in it, it should break loose without a problem.
The 2 shoulder bolts that hold the rocker arm cover on the UCE are a 5mm hex drive.
When I removed the covers to stop a slight oil leak.
I set my Snap On torque wrench to 7 ft/lbs but it probably took 10 ft/lbs of torque to break them loose.