VY Equipe Fuel Sender Problem

[Robbo VS3]

I have a VY V6 that seems to be having trouble knowing how much fuel is in its tank. The fuel warning comes on when there is still 20 litres in the tank and the needle drops rapidly after filling the tank full, so its giving me a completely false reading.
If this is a fuel sender failure, where is it located and is it difficult to replace?

Thanks