If the door is in good condition, consider reusing it. You can advertise on sites such as Freecycle and Freegle. If you are getting new doors, ask if the installers dispose of or recycle the old ones.
Wooden doors
Remove glass and place in the non-recyclables (general waste) skip available at all recycling centres (except Brechin).
The wood goes in the wood skip (available at all recycling centres).
UPVC and aluminium doors
These usually come as a unit, making the glass difficult to remove. They can go into the non-recyclables (general waste) skip at all recycling centres (except Brechin).