If you want to re-use the rubber line you will need a flare nut wrench. You would have the proper size if you bought a good quality complete set of flare nut wrench's.
DO NOT TWIST THE RUBBER HOSE!
Steps
1) Remove steel inboard line with your flare nut wrench.
2) Remove rubber hose bracket from frame or rubber line metal end from bracket which ever is easier. Most time it is easier to take bracket off frame.
3) Using the proper 6 sided flare nut wrench unscrew wheel cylinder metal end of hose from wheel cylinder, this should be done with a 1/4 turn (crack) of the connection then you should be able turn hose by hand carefully to unscrew it. No extreme bends or twists!
From the above picture the hose doesn't look that old by the shiny end but on older/original where you will be replacing the wheel cylinder and hose it's 'Open Season' as they say especially if someone has monkey wrenched the wheel cylinder end nut, (used opened end vs flare nut wrench) so cutting the hose to use a six sided socket to remove is OK. If it is really old & rusted/frozen a little dot of red hot heat on wheel cylinder will loosen up 'jist'bout anything or just torch it off.
In just about all cases you will need the get the rubber hose metal end off the wheel cylinder to remove the wheel cylinder from the backing plate.
Question? Do you mind if I ask you what you do for a living? The reason I ask is because "but its happy where it is." kind of puzzles me.... lol