Servicing undersink ceramic water filter

I have a 3 cylinder Doulton unit under my sink. I'm at a loss how to get the cartridges out. The water stream from the faucet is nearly just a trickle now and I really need the filters changed.

I have the replacement filters, but just cannot figure out how to get the plastic sleeves undone. I didn't get any instructions when my plumber installed it and he came over about 8 months ago and took the filters out, rinsed them and that did the trick (the unit was only in about 12 months).

I got as far as the top off, took out 8 screws, a plastic piece came off the three cylinders and then I see these cylinders have a rubber seal holding them into the unit. So, I just put it all back together and now I'm really frustrated because I just don't know what to do. My plumber is out of commission so I can't get him to help. Can you??

A: 1. Shut-off the water to the filter. Open the filter faucet up to remove back pressure built-up. Wait 10 minutes.
2. Unscrew the filter housings (turn left (clockwise direction if underink). There should be no reason to remove any screws. The screws are only meant to mount the filters to the bracket. The filter housings are the white canisters that have the cartridges inside.
These are simply unscrewed so you have access to your cartridges.
3. Unscrew the filter cartridges and replace with new ones or just clean the ceramic candle (most likely labeled Ultracarb).
4. Put everything back together and turn shut-off valve back on.
Inspect for leaks.

Here is a link for ceramic water filter cleaning instructions

Customer feedback:
Thank you for providing these instructions!  It worked!   The problem was that the plumber that installed the unit had the cylinders screwed in so tight I could not budge them.  I was able to get someone to look at the unit this past weekend, he was able to get the cylinders detached, I was able to flush the filters and now the unit is working just fine!  I love this water filtration system!!!  My water is horrible and even with a water softener, I won't drink it.  However, with the Doulton filters, I can drink the water!  THANK YOU for a terrific product!!