In ordee to upgrade you need to put files at correct location
Do not copy and paste upload folder to root directory and expect it will upgrade.
To have upgrade u need to place files which are inside upload folder to root directory if forum is installed directly on domain else in sub directory where xf is installed.
When u paste the files to server the prompt will come for skiping or overwritting the files on server.
U need to overwrite all files which are asked for successful upgrade.
Note: take backup of file and db, before performing upgrade