there are a few good ways already mentioned. for factory glued inserts, they use super glue, so the drill bit method. for most everything else, its hot melt, so a lighter and pliers. if epoxied, its a really depends how much was used if it will work at all. most likely, the arrow will be ruined.
with the drill bit method, it helps a lot to NOT have a field point in there, just the plain insert.
depending on arrow length, you can just cut the shaft behind the existing insert as well. i shoot a 27" arrow, so when i get ones that are factory glued at 31" or 29", i just cut the arrow and toss the old insert. i use brass inserts on all my arrows.
when using brass inserts, use hot melt glue, then its as simple as a lighter to change/remove them. brass is soft (so is aluminum) compared to the steel drill bit, so you can mangle the backs of the inserts.
3riversarchery.com is where i get all my brass, $12 a dozen, so its cheap. their 100gr inserts are not threaded in the rear section where the 50gr ones are. (for FACT weights)