Not a job to consider if you’re a bit unsure - there’s a real safety risk if you do something wrong. (By the way, you should bleed your brake and clutch systems, and replace with brand new fluid, at least every two years. It’s a tricky job and best done using a specialist brake bleed kit. Or a mechanic.)
You’ll need a torque wrench and the torque settings for the caliper bolts, new pads and some copper slip or brake caliper grease.
Wear thin disposable gloves. And avoid breathing in any brake dust.
Give the bike a wash, using car shampoo (not dishwash liquid) especially around the calipers.
Then refill your bucket and find an old toothbrush.
Loosening caliper bolts will require a socket or Allen key insert and a long, hefty bar to crack the nuts loose. If pads are secured by threaded pins, slacken them off first.
Pads are retained by a pin, either threaded or secured by an R-clip.
Manoeuvring the calipers out is often a bit of a squeeze but wheel removal isn’t usually necessary. Pulling the pads back with your fingers can help - don’t lever with a screwdriver or you could damage the disc or caliper. Remove the retaining pin and note how the pads, pins and spring backing plate all locate. Slip the pads out.
Squeeze the lever gently - enough for the piston to just show in the caliper. If one doesn’t move so freely, hold the free ones back while squeezing to move it. Don’t squeeze so much you pop the piston out.
Scrub everything with soapy water and the toothbrush, including the pins and spring plate.
You’ll need to squeeze the pistons right back into the caliper to fit the new pads. Undo the top and put an old towel under the reservoir in case brake fluid overflows.
Squeeze the pistons back into the caliper, keeping an eye on the rise of fluid in the reservoir.
Put an ultra-thin smear of copper grease on the back of the pads and the retaining pin. Make sure none gets on the pad surface. Replace the pads, spring plate and pin one side at a time, then slot the caliper back over the disc.
Do the caliper bolts back up finger tight. Pump the lever until the pads make contact then, keeping the brake lightly applied, spin the wheel in the direction of rotation to help seat the calipers.
Next, pump the brakes on hard and nip the bolts tight. Repeat both sides and tighten to the correct torque setting.
Bed your new pads in over the first hundred or so kilometres by avoiding overly light or overly heavy braking.