trying to replace my pads. which bolts do i undo? sounds silly i know

You need to undo 2 13mm bolts on the caliper to remove it but you need a special tool to wind back the brake piston, If you havent got one of these you will struggle to do it.

Yes. Also I was watching and reading a few guides, some say take some brake fluid out some don't Obviously it'll be a lot less hassle to leave it in but what's best?

The fronts have 7mm allen key bolts as I found out yesterday and I only had a 6mm allen key Plus the screwdriver bit I had only fit my screwdriver and couldn't get the leverage to undo it so have now bought an adapter for thre ratchet . Another week to wait

Think the bolts are on the backside of the rear calipers 13mm?
And I left my brake fluid in

Only need to take fluid out if you have been topping it up due to the pads getting low, cos when you push the pistons in you will force fluid back into the reservoir so might overflow.

Yea take the cap off under the engine bay make sure it doesn't overflow