Block paviour manhole cover is too heavy for me to lift (I'm old) What is the easiest way to either get a lighter one or will it be necessary to rebuild the top of manhole ?
I guess you're talking about the frame type covers filled with blocks?
It's not so pretty, but you could simply remove the frame completely and replace with a simple lightweight galvanised cover.
Any Builders' Merchants would have them. Just make sure you go for a "pedestrian" or "heavy duty" cover if it's driven over.
You'll need a bucket of sand & cement to bed it in.
Go on... you can do it :o)