Login no longer works

I have been rebuilding my website https://www.promovideo.co.uk using wordpress and have installed the new site at https://www.promovideo.co.uk/wp. I now want to move the wordpress site to my main address https://www.promovideo.co.uk and overwrite the old site. I changed the wordpress address (URL) in the general settings tab and clicked save. I now can’t login to the site with my username and password. I get the feeling I’ve done something very wrong! Please help