Need to know how to remove hood hinges that have factory welded or glued to firewall, 1993 ford ranger?

Most are spot welded into place. The only way to do it is to cut them out, using a grinder to remove the spot welds as best as possible then removing the hinge with a dead blow hammer, or use a metal chisel to help dislodge it the rest of the way

Search for "spot weld cutters"-they'll do a much quicker, neater job than a grinder. Essentially like a hole saw for wood or drywall only a lot smaller and hardened for cutting metal. Here's about the cheapest to be found that works well-

http://www.harborfreight.com/3-8-eighth-inch-double-sided-rotary-spot-weld-cutter-95343.html