First off, it sounds like you probably didn't have a written contract.
Based on that assumption, I further speculate that you probably had a verbal agreement.
Now, if the agreement was specifically "give me a reduced rate and you can put your name on the website", then no you should run any changes past him, and work out a different agreement if he doesn't want his name on it after your changes.
If the verbal agreement was simply "make me a website for £X amount" then change whatever you like, and as a courtesy notify him of the changes and offer to remove his name if he is unhappy with the changes.
I think though, that in the second scenario you have no obligation to notify him of the changes or remove his name.
However, if there is a written agreement it should be in there.
Personally, I'd remove the name if allowed as it likely adds nothing to the purpose of the website.