Here is a crappy how to remove the EF and EF-S baffles (this is at your own risk!) I saw it somewhere and copied it for later use.
1. You will need a small Phillips screwdriver screw driver
2. There’s a raised screw on the side of the metal lens mount about 15 mm to the left of the electrical contacts that retains the baffle.
Undo it. (Don’t undo the two inset screws that retain the electrical contacts.)
3. Remove the four screws on the rim of the lens mount that hold the lens mount to the lens body. (don‘t hold the lens by just its barrel once you’ve removed these four screws)
4. Gently lift one side of the lens mount upwards at the point furthest from the electrical contacts, enough to be able to get your fingers underneath. (Note: the lens mount won't move much near the electrical contact owing to connecting wires – so don't try pulling the lens mount off.)
5. Push the baffle out of the lens mount from underneath whilst holding the lens mount firmly, taking care not to pull out the wires (note: the wires are firmly attached, so this would take some force). The baffle’s held in (not very firmly) by four plastic clips, and will ping out when pushed from behind.
6. Reassemble. (Note: if you’re replacing the baffle with an EF one, this can be added after reassembling the lens).