What kind of panel is it?
FPE or Zinsco - dangerous panel! Changing breakers isn't enough! Replace panel soon, or replace innards with Eaton kit
Challenger - panel fine, breakers bad, replace breakers with BR
Alien (wrong-brand) breakers in panel - research to see if they are UL-Classified for your panel, if in doubt replace the misfit breakers... not worth smoking a bus over a $5 breaker
That's not brand loyalty. Breaker busbars are different, and wrong-brand breakers may snap in, but won't clip on properly and will arc and burn the bus.
- Split-bus panel of any brand
Both obsolete. Split-bus panels are a little risky but not worth getting excited over. See if you can install a new main panel right next to the obsolete panel -- and make the obsolete panel a SubPanel. That will solve the problems and only requires moving about 8 wires (big wires). You can add any new circuits into the new main.
- Cutler Hammer CH (now Eaton)
- Square D QO
- GE Qline
These are top industrial grade panels and fully supported. Keep them, enthusiastically!
- Murray (now Siemens)
- BRyant then Cutler Hammer BR now Eaton
- Square D HOMeline
These are not industrial grade but they're perfectly fine panels and fully supported. Keep em.