Large houseplant fern needs TLC (Woolton L25)

Help is needed for this large houseplant fern so I'm hoping somebody with green fingers can give it the care it needs.
I've had the fern for many years and have tried different locations and conditions in the house but it never seems very healthy.
It has numerous brown patches on its leaves as shown in photos but it does still produce new leaves.
It's currently approx 40 inches across so is quite big.
I hope someone out there can give it a new lease of life!