Bought my first road bike last year. Didn’t know what I was doing -still don’t, clearly!

The bike is set up with a 39/53 chainset paired with 12-27T cassette.

Is this a race set up?

Sometimes I struggle on a couple of steep climbs – Holden Lane out of Silsden and Otley Road out of East Morton.

What difference would be felt going to an 11-28 cassette?

The difference would be tiny.

If you are stuggling with steep terrain you might want to look at a triple or a compact chainset with smaller chainrings

Appears I know even less than I thought – the chainset is 50/56.

Is this not a Compact?

Do you mean 50/36?

Here is the spec for my bike :

http://www.westbrookcycles.co.uk/bikes-c5/road-bikes-c18/scott-addict-r3-compact-drive-road-bike-2010-p28115

– click on specification….

Looking like it is 50/34…wrongly assumed that Shimano 105 FC-5650 meant 56/50. All very confusing!

So your choices for lower gearing are either swap to a triple (but you’ll also need to change the front mech). Or fit an mtb cassette with something like an 11-34 range but this will make the steps between all the gears larger