I've got a pair of Chatsworths and have changed the grill cloth a couple of times , it's not difficult .
First you need to remove the beading around the front , this is glued in ( in my case there wasn't much glue ) gently prise these off . I carefully tapped the centre of one of the longer pieces with a small hammer against a block of wood until the glue started to break then it was easy to pry the beading off .
The cloth is then stapled to the cabs , just pry the staples out and the cloth will come off . I found that vintage guitar amplifier cloth makes a good replacement
( mine has the cloth from a Fender blackface ) . Use the reverse of the above to fit the cloth , then when finished use a hairdryer to waft hot air over the grill cloth this will pull it tight and take out any sags .
Just thought it'd probaly be a good idea to take the drivers out before doing any of the above .