Why change the bearing, and not just order a new pulley?
It's about the money you save. A new bearing and a few bolts and nuts cost you less than $10, but a new pulley is going for $30 or more.
Once you prepare your pulley, it becomes way easier to change the bearing next time it breaks. Maybe this time you can change the bearing in time, and you don't wait until it seizes? So if your mower sounds very loud and ruff once you engage the cutting blades, maybe it's time to check the bearings on the deck?
Learn how to drill holes in steel, and how to drill out rivets, and spot welds.
Many idler pulleys are riveted, and it is not possible to exchange broken bearings. Once you drill out the rivets (you learn here how to drill out rivets), you can separate the pulley into two halfs.
Sometimes they don't want you to go the cheap route, and they spot weld the pulley. Now even with rivets removed you are still not able to separate the two discs. I show you how to prepare the spot welds, and how to drill them out best.
Keep a few mayor rules in mind. Drill a small pilot hole first. Small drills need high speed rpm, and then drill with the large drill. The larger the drill, the slower the drill speed. If the metal you drill is very thick, you may have to use oil, or some other cooling fluid while you drill. Most important for your safety for larger drills. The pulley needs to be mounted firmly in order to avoid it spinning uncontrollably when the drill makes it through the material. (You'll see, i show this in the video.)
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Enjoy and good luck with your repair!