Changing Shimano Tiagra 12-28 cassette to 11-32 I currently have a Merida Scultura 300 which comes fitted with Shimano Tiagra 50-34 crankset and 12-28 cassette. I'm struggling up some big hills in my area and want to change to a 11-32 Tiagra cassette. Is this a straightforward like for like swap or do any alterations also need to be made. Thanks in advance
Assuming you have the latest 4700 series 10 speed Tiagra. We can look up the rear derailleur specs here.

If you have the long cage GS model derailleur you can go to a 11-34 cassette, if you have the short cage SS model you are limited to an 11-28 cassette.

I'm guessing that because your bike comes with a 11-28 cassette you have the SS model, but Tiagra derailleurs are not expensive, relative to other groupsets, especially if you look for as new take-offs or low mileage used examples.

You will of course need to change the chain as a longer one will be required, and new cassettes should only be used with new, unworn chains.