- Separate them from the rim for spacing.
- Separate them from the rim for wheel removal.
- Separate them from their holders for replacement.
Which?
1. Usually there is a barrel adjuster on the part of the caliper you didn't get in the picture. Screw it in some to open the gap. If no barrel adjuster on caliper or brake lever then undo the cable from the pinch bolt.
2. Some have a release on that part of the caliper you didn't get in the picture that you just flip and it opens much wider so as to let the wider tire pass. If no release, deflate the tire or turn the barrel adjuster all the way in.
3. That's for others to answer. I usually just replaced the entire pad and holder.
Centering next?