Website Administrator Lost!

My father has a photo studio and we hired somebody to build a wordpress website. After the website was finished he only gave us one account with publisher rights and now the original administrator is nowhere to be found and we can not update our wordpress site nor make any major changes with CSS or anything…

How can we regain control of our website so we can update it regularly without needing the administrator. We won’t ever find this guy again and we don’t want to have to delete the site from FTP and start from scratch…

is there any solution?