Re:
I'd assume it's a 1 1/8 headset so you'll have plenty of options, just depends on your budget. You'll find plenty of cheap options on Ebay or you could (should) get something decent. Cane creek, hope etc.
You'll want an external cup version, so no inset/zero stack ones.
Assume you know how to remove and fit, but if not.....
Removal:
Using a headset removal tool (assumed you have remove stem.and forks at this point). Slot the tool through the steerer tube until it goes clunk. Tap firmly with a mallet until the cup is free. Repeat on other cup.
You'll want to remove the crown race from the fork steerer. This can be a pita if it is not a split race (which you can just ease off by hand). Otherwise you'll need something to prise it away from the fork crown and up the steerer tube. Be careful not to damage your fork when doing this. Often forks have a slot to help you get started, you 'could've use a screwdriver and hammer. I prefer to use something metal and slim between the fork crown and headset race and work round gently forcing the race away from the crown.
Fitting new headset:
This is best done using the proper tools. You can bode your way through this using various things, but the proper tool will press your new cups into your frame gently and accurately, and if done right will not cause any damage to frame of new headset. Crown race (if split type) will slide down your fork steerer tube. If not split you'll need a tool or method to get the crown race seated properly at the bottom of the steerer without damaging it as it is what the bearings are in contact with.
Assembly:
Slot your forks back through the head tube. Refit spacers and stem. Unless your new headset is exactly the same stack height as your old one, you may need to add/remove spacers so when your stem is refitted, it sits a few mm above the top of the steerer tube. Fit the top cap and bolt, tighten up so that there is no play in the forks and the ly can be turned smoothly. Dont overtighten as you will damage the bearings.
Once happy, line up the stem with the front wheel and tighten up the stem bolts.
Fit your wheel and all done.
With the right tools, it's a 5 minute job. Tools cost a bit so if you think you'll only do this a few times in your life, dont invest in them and get your local bike shop to do it. They shouldn't charge a lot.
