First job, get the hair trap out (might be a pain due to silicon bodge but it needs to come out)
Second, cut the wastepipe where its visible and got a bit of clearance to the joist- middle of that gap would be about right (have a dish or pan ready to catch any water)
Then, pull the pipe stub (thats in the trap) across the gap between the joists (this should turn the trap anticlockwise about 10 or 15 degrees)
With luck you'll now be able to unscrew the top of the trap (couple of long bolts through a bit of stick spaced to fit into the plughole usually works).
Remove the trap, washers etc, see whats what. Bit of luck whoever fitted it didn't go mad with silicon, if they did you'll have to get rid (silicon remover works v well).
See if you can buy a replacement trap that is a bit shallower and slightly smaller diameter (on the trap, not the bit that butts to the shower)
You've done the hard bit (getting access to the waste pipe)- unless you know a trustworthy plumber (and I don't include checkathing or any of the other subscriber-driven sites) then you'll end up paying some chancer £200 for 10 minutes work and a £12 trap from Screwfix. You'll be making the floor good anyway, right now you've nothing to lose by having a crack at it yourself
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