What is the material, PLA or PETG? I have had luck modifying PLA. You can use a fine toothed razor saw to cut it but go slow, if you generate any heat then the PLA starts to soften and will grab the blade. Same thing with sanding.
Putting it all back together is a different matter. If you don't mind seeing the hinge then you can follow Cruzer's tutorial in the Jango section. If you are going for a screen accurate look and don't want to see the hinge, there are still a couple of options.
You could glue in elastic with E600 on both sides of the inside gauntlet and it will have enough give for you to wiggle your hand through (probably the best method since you can already put on one gauntlet)
Or
You could glue in hidden piano hinges. One side would have the loose pin for opening and the other side would need to be a flexible hinge. Because of the way my gauntlets were modelled I needed to be creative with the construction of the flexible hinge and I had to glue in elastic. My setup works great for me and there is no chance of these ever slipping off. My gauntlets are also extremely close fitting so I knew I wouldn't be able to make a full elastic closure work, I really have to stuff in my gloves.
