The fittings are simple, you just have to push the "ring" or "collar" that is around the fitting in and that releases the grip on the tubing. make sure that if you do force the tube out of the connection by pulling on it very hard without pushing this collar or ring in that you cut the damaged part of the hose off and start fresh when re-connecting otherwise you will have a high risk of leaking because of the damage brought on by not removing the hose properly from the fitting.
https://www.youtube.com/watch?v=-Avzf-jsHyM
As for removing the cap on the RO canister I do as others have stated above and simply remove the hose and just unscrew the cap quick and simple.
HTH
Trevor