I'd bend the brackets a bit more to the outsides and then the CPU can be lift out. I'm not sure how these brackets actually work.

Just clean it with compressed air from all sides. Don't let the fan spin excessively fast when doing it. Cotton swaps are good for fan cleaning.

It can be disassembled. The CPU cartridge locks into the slot 1 mounting brace by the visible notches on each side of the CPU PCB. Your fingers are all you need to get it to release. The plastic heatsink shroud snaps to the heatsink at the 4 flat indented corners. A flat screwdriver would work to release those. But I wouldn't bother taking it off. Remove the CPU from the motherboard before trying to remove the shroud.

Just use canned air and blow backward to normal fain air flow. From the left and right sides. Keep a gentle finger on the fan so it does not spin.
No need to remove cpu unless board does not boot.....those are cheap odd slot mounts....

My advice:
1. Disassembling things has the risk of breaking them. A lot of parts have plastic tabs that will snap, as they are brittle with age. The retention brackets on my P3B-F actually exploded when I took a CPU out last year. It was so shattered that there was no hope of supergluing them back together.
2. With that said, most retention brackets that I've seen have two mechanisms for locking: Tabs that you press in while you slide the cartridge up or a slide.
3. That looks like a retail/box version of the Pentium 3. Getting the shroud off is easy once you've done it a few times and kind of hard when you're doing your first one. Just look at it from the side and you'll see how it's attached. It requires more force than you think to get it off.