Is it straightforward to swap a 50/34 chainset for my 53/39 one? Would the front mech need moving or changing? I have a 9-speed 105 system. Do chainsets with hollow tech bottom brackets mean I would also have to swap the BB?

Sorry if these are stupid questions…

Dead easy – remove pedals, remove left crank, tap out chainset, replace with new, fit pedals, drop front mech down a bit, set up front mech, maybe remove a link or two from the chain.

BB stays in and you gain a spare, Shimano techdocs is your friend, or Park Tools website, or Sheldon, or…

I’m guessing your older 105 uses an octalink bb ? ( are the bb cups on the outside of the frame ) ?
If it does you will need new external one if you get a modern chainset

A lot of road chainsets are sold without the bb unlike mtb ones

Thanks guys – I might go for it then, its to help climb. Will check the octalink thing but I think it is one of those