While I think you'll be smart to hire an electrician and consider replacing the whole panel...
Circuit breaker boxes vary in style. You have to buy the correct replacement breaker for your specific box. To determine what you need, examine the box itself. Somewhere on the box will be the name of the manufacturer.
Tip: "Square D" is not it. (Personal experience talking) - Square D MAKES breakers to fit numerous types of boxes.
If you can't immediately find the name of your panel maker, go to this link:
Online site for buying circuit breakers
They list a lot of manufacturers there - see if you can find yours.
Now again - because you yourself said you're scared to remove it - PLEASE DON'T. This is potentially deadly work you're considering and if you don't know what you're doing, this is NOT a project you should learn using the trial and error method!!!
Update - after looking at the extra pics - your breaker box is by "American". First manuf. on the list. The labels on some of your breakers indicate it.