WordPress Address Change

I’m new to making a website, but I created one through a guide on youtube (hosting through Host gator). After making the website, the youtube guide said that I can go to (websitename.com/wp-admin) and log in, settings, general, and put a “www.” on my wordpress address URL.

I figured at this point that it might be a good idea to change the domain name, not realizing that it wouldn’t work. Thus, I changed my host name from http://www.tomorrowconstruction.com to http://www.architechtureofthefuture.com and I am no longer able to go back to change it.

Can someone please help give me a solution on how to fix it?