My road bike, an old Look KG 231, has 53/42 chain rings and a 13/26 8 sp cassette.
I frequently struggle on steep hills especially if they are long because I can’t find a gear low enough to spin in. (maybe I’m just a wuss)
Can I swap the cassette out for one with a bigger range?
I have seen 8 sp 11-30 cassettes like the Sram PG830 but this is a MTB cassette. Will this fit a road bike?
Or is the only option to try to change the chain rings at greater expense?
Any advice appreciated.
Thanks.

Pretty certain you’ll be stuck with 26/27’ish. Not 100% sure as eight speed goes back a bit now.
Seems the further you go back the smaller the cassettes?

Edit; You should be able to fit a 39t ring.

The mech is likely to limit it to a 28.

39t ring will fit. Long cage or mtb mech and 34t plus a couple of links/new chain may be best bet