Need to uninstall and reinstall wordpress to main domain

I don’t know the version of wordpress it’s hosted through aplus.net.
How do I uninstall wordpress and reinstall on main domain name through aplus?First of all They told me there were two different ways to set this up. They said the first was to redirect wordpress to point to the main url, then the second way was to I guess just add wordpress to the main domain name. I told them I didn’t care as long as I could upload my own theme which was the whole point of doing this. I have a theme I want to upload. They set it up the first time and I was able to upload the theme,5 minutes later the site went down. It’s been 3 weeks of trying to get help to get this thing up again. I told them several times I wanted to do it for the sole purpose of adding my own theme, however, the 2nd installation was done wrong in that it was not set up on my main domain and I could not upload my own theme. They no longer will help and I am trying to get help somewhere on this planet. Is there anyone there that can help guide me through the process since I have zero experience of building a blog. I deleted most of what was in the files and uninstalled wordpress and deleted the username in the SSQL thing but not really sure if I deleted everything. There might be a file left in there but wasn’t sure if I deleted it if it would possibly mess up the entire website. I have no content on that particular site so just want to set up a blog form scratch. However, I do have 2 other websites on that hosting that I need to be careful of not getting deleted.