Replacing HTML site on root domain with wp site


I have an old html site on the root domain: let’s say and I have created a new wordpress site in lower level folder:

I want to replace the old html on root with the wpsite. How would I accomplish this with the least amount of problems.

Can I go into pydio and delete all on the root and then just move all in the lower folder into the root folder?

Or do I have to delete all in root and then do a 1 click install on root for wp and then move everything?

I use wpbackitup so I would love to just be able to restore a backup from the lower level folder.

Please let me know what I have to do.