Are they easily replaceable or do I have to buy new frames?

[Barney]

One of the little plastic nose-protector things on my glasses is breaking.

[Barnhart]

As you have mentioned, one of the little plastic nose-protector things on your glasses is breaking. You can go to the glasses stores where you buy your glasses and ask the technician there if the broken plastic nose-protector things can be replaced. If the answer is no, then you have to change a new frame.