Upper wheel assembly

The rollers for the upper rack have broken on my Kenmore upper wheel assembly. I have the replacement parts. How do I take the old ones off. I initially tried a flathead screwdriver thinking they would pop off, but that did not seem to be working. I did not want to put too much pressure on them in case there was another method.

I cannot figure this out either.
The rollers for the upper rack have broken on my KITCHENAID upper wheel assembly. I have the replacement parts. How do I take the old ones off. I initially tried a flathead screwdriver thinking they would pop off, but that did not seem to be working. I did not want to put too much pressure on them in case there was another method
THANK YOU