Cleaning AGP that hasn't been cleaned/covered in 3 years

I am trying to clean an above ground pool that hasn't been cleaned or covered in 3 years. The pool is about 24 foot. We use a sand filter. We need to get as much debris out as possible but I am not sure what to do after that. There is a lot of sludge and the water is dark brown. Will chemicals and pumping do the job or do we need to try and drain it and start over?

Thanks.