Can I replace a 15amp breaker with a 20amp breaker?

No. You can do it the reverse way, and it will still be safe, but will have less capacity, but replacing a 15 with a 20 is a fire hazard.

Not unless the “wires” on that circuit will hold 20 amps.
it would have to be a ten gage wire….,
the wires on a 15 amp circuit are generally 14 gage or at most 12 gage.
If you run all those extra watts on a #14 or a #12 wire, that you have changed over to a 20 amp breaker, it would over heat the wires and could cause a fire.
An electrician could check out the wires and let you know for sure.

Does it have a three prongs on the end of the humidifier? If not buy an adapter with three prongs (adapter) and see if that works. It worked forme many years ago when the air conditioner keep blowing the fuse. It worked.

Whoever designed and buit—and wired—your house intended that circuit to be a 15A circuit, and installed the appropriate breaker. If you “pretend” that it’s a 20A circuit and install that breaker for convenience’ sake, then as @pdworkin says, you risk the entire structure.

What you can do, and it shouldn’t be expensive, is install a new, dedicated circuit for your AC unit and install a separate breaker for that. Since you’re asking such an elementary question, though, you should definitely have a qualified electrician do this.

According to the size of wiring that is on the breaker. A 20 amp breaker would take a 2.5 or thicker wire. Call an electrician for saftey.

Is it tripping the breaker or is it the ground fault circuit interrupter (GFCI). Just had the electrician out because I kept tripping the GFCI, bad one needed to be replaced. The electrician said that cheap GFCI’s fail about 5% of the time with nothing wrong.

CALL an electrician and get it checked out.

Nope. You live in an apartment, and the wiring in those is never heavy enough for that upgrade, and no apartment manager will make that improvement possible.

No! Not only will you cause a fire and possibly kill people but your tenant’s insurance will not cover you! A humidifier should not trip a 15A circuit by itself. If your oven is electric, try plugging in to the accessory outlet if there is one. Try and find an outlet with less already on it. That may work.

There have been alot of good answers already. If the wire is a #14 keep the 15 amp breaker in place. Technically according to the code book from what I remember a 15 amp breaker or any breaker is only suppose to be loaded up to 80%.

I hear lots of older wire is from a more pure copper source and even a better conductor than what the copper clad wire the sell today but still can be over loaded easily. Sadly most of the good pure copper did not have a ground wire.

So, not 15 amps but 80% of 15 is safe. My math is rusty but I come up with 12 amps safely on a 15 amp circuit. I would see if I could eliminate anything off that circuit at least possibly just at night while the humidifier is working.

You just never know what kind of birds nest you can be getting into when it comes to wiring especially when alot of home owners that have little experience start trying to be mister fix it. And/or a Mr. prideful green Electrician that merely thinks he know how to wire something just because it works (for a while). lol Actually that’s not really funny!

Please be extra careful. The National Electrical Code book is actually put out by the National Fire Protection Agency for a good reason :-)