Bite the bullet..... but you'll need to bear a couple of things in mind, and have the right tools. The tools will cost what it would cost to have the job done at your LBS, unless you are an experienced eyelash flutterer, or take baked goods along as a bribe........ and you only need to buy the tools once!
Firstly you need to remove the old pedals. They'll either have spanner flats or allen key slots, or both. The spanner flats will be 15mm, so you need the right spanner, and a specific pedal spanner is better because of its shape, but not compulsory. The allen key slots will be on the inside of the pedal axle and will either be 6mm or 8mm.
The pedals are threaded differently on either side. On the drive side (right hand side) it's normal threading, so you need to turn the spanner anti-clockwise to remove it. Easiest way to remember is to set the crank arm so it's facing forwards at 3 O'clock. Put the pedal spanner on at 12 O'Clock and push towards the back of the bike to undo it. Put the chain on the biggest chainring and cover it with a rag before you try to undo the pedal, as this reduces the chances of spanner rash as the spanner slips and sends your knuckles towards the teeth of the chainring! It's likely to be stiff to remove, so be prepared to us quite a bit of leverage.
On the left, or non-drive side the thread is reversed, so you need to turn it clockwise to undo it. Again, put the crank horizontal with the pedal towards the front wheel, the spanner vertical and push towards the back wheel to undo it.
To put the new pedals on make sure you know which is left and which is right. It'll be marked on the pedals, but with your A520s it should be obvious. (the squarer end is at the back with the mechanism facing upwards. ) but to be certain look at the spanner flats where you'll see an L or an R . Clean the internal threads on the crank arm with a squirt of GT85 or similar, and apply a layer of grease or coppaslip to the pedal threads. Start on the right and start off the thread by hand. Do this reasonably carefully, as it's easy to cross-thread them. If it doesn't feel right stop and start again. You should be turning the thread towards the front of the bike. Snug it up by hand then use the spanner or allen key to tighten it properly. It needs to be quite firm.
repeat on the non-drive side, again, thread by hand turning towards the front wheel.
Hope this helps.