@Khayman I would recommend watching this video multiple times, I probably watched it 4 times before the change, then actually watched it during my change, pausing when I was going too slow to keep up. Don't try to keep up, just pause it.
Along with the bearings, I also bought a bearing pull kit, one with 1mm increments so I was guaranteed to have the exact right sizes.
If changing your bearings is not an emergency, then look hard to find someone with a proper press. I cannot stress enough how important this is. I was unwilling to ride my OneWheel because of the sound; I didn't know if I was destroying it from the inside. In my life, this constituted an emergency, and I made due with the bearing pull kit and what I had around my house. All of my stress for the change came when setting the bearings. My hope is to never go through that again and change the bearings before I start experiencing any issues.
If you have changed the tire before (I have done so twice now) it is only incrementally harder to add the additional work to disassemble and reassemble the motor. The really "hard" part is probably less hard, and more nerve racking if you don't have the skill. As I described earlier, it is setting the new bearings in place. After that, the next hardest part for me was getting the silver screws off of the axle, my allen wrench was bending a lot, because they were so tight. I was becoming afraid it would break and was just about to go get my safety goggles and gloves when it finally budged.
Watch the video, and, if possible, find someone who has changed bearing before to help you. Then, it isn't so bad.