I didn't read the full 6 pages on the "How To" link but you should relieve the fuel pressure first before attempting to change the filter. 45 psi 'approx' fuel pressure can do harm to you if it hits your face, eyes, hot exhaust pipes, etc. Just pull the fuel pump fuse, crank the engine over a few seconds, it won't start. Turn key off, reinstall fuse, change your filter. Even after relieving fuel pressure there will be residual fuel in lines leaking when removing the filter, so have rags handy and be safe.
From my experience the plastic tools don't work very well. Asked at the parts store for something more substantial and they had a metal tool that looked like scissors that had a shaped cup at each end to fit over the fuel line with each end a different diam. Gives far more leverage and something to push with in tight quarters!
Hope that helps...
Sometimes there's dirt/rust forms inside the connection. Try spraying it out with wd as suggested above. In a kind of awkward movement for one hand, I have the tool positioned on the line, then I try pushing the line into the filter, then I press the tool into the connection. I then tug/twist on the line with the tool still pressed in while holding the filter with the other hand. I have used both the nylon and steel scissor tool as mentioned in other reply but prefer the steel tool better.
The scissor tool is made for two different line sizes.