Change a lighter fuse

I assume you mean the wick. 

In a Zippo lighter, this is easy – remove the inner piece from the shell, unscrew the bottom, and feed the wick through the hole.

Bics have no wick, working similar to butane lighters.

If that’s not what you’re talking about, then perhaps you mean the flint, which is the piece the wheel rubs against to spark the flame.

Here’s a diagram:

If the spark wheel gets stuck, the problem is the flint is gone and the wheel is now rubbing against the flint spring. When metal hits metal, it locks, which is why you need oil in an automobile engine.