Help with clearing existing database and one-click installs

I am totally new to web hosting world. I do know a bit of web designing and I thought hosting would be easy but now it seems like I’m in a strange world where everyone knows what’s going on except me.

I want to upgrade to the latest wordpress version.

What I did so far
[]I tried doing the 1-click install by using the same database and no directory. I got an error email telling me the database isn’t empty.
]I did the 1-click install again, this time using the create a new database option. I got the same error.
[*]Third time, I found this video of a lady who used the directory “demo” to install. For example " I did that and upgraded to the latest version but its the “demo” directory only. When I go to the main site address, it is still the same.

I am lost and have no clue whatsoever on how to upgrade to the latest version. Please help!

Hope this helps a bit