You have 'press' connections
You can not 'remove' a press connection........you cut the PEX behind the fittings. (PEX is distorted/damaged inside connection when it is pressed)
As for replacing that Cold Water Inlet Valve.......
I would cut the PEX on cold water line on supply side of 'T' and Bypass line side of 'T' then disconnect cold water connection at WH and redo that whole section using Shark bite 'T' then some new PEX pipe (you can get a 2' section) to new shutoff valve and elbow to make connection at WH inlet.