Unfortunately bangles are only really designed for people whose hands and wrists fall within a particular size range. When I was trying to be fem, I couldn't wear them because my hands are tiny and they basically fell right off if I moved wrong.
If they're very close to fitting though, you could try to get them on and off in the shower (seriously). Warm water and soap will lubricate your skin, and the heat will cause the metal bangles to expand slightly, and between those two things you just might be able to do it. I've been able to slide things off my wrists that really weren't supposed to slide off by using the shower trick.