If you can buy, or borrow, a set of hex wrench sockets like this https://www.amazon.com/LEXIVON-Complete-32-Piece-Enhanced-LX-144/dp/B07MDLCLML/ref=sr_1_5?crid=ZVWAMSNUN6BN&dchild=1&keywords=hex+wrench+socket+sets&qid=1611858703&sprefix=hex+wrench+sock%2Caps%2C224&sr=8-5 you could then use a breaker bar to loosen the bolts. You'd also then be able to use them to make sure you get things tight when installing the new crank arm.