Hi there,
I think the problem here is the installation itself, and it fails. I tried it multiple times too and it fails in the middle, hence, creating incomplete files. Retrying it will only display error that it’s already existing because it is, just incomplete. Deleting it again will just repeat the issue once you install it. The best workaround, for now, is install it through FTP, by downloading the files from Themeforest and extract the revslider zip package and upload the folder.
And the only one who could help you with installation issue is your hosting provider. The theme only provides the files that are needed to be installed, and Wordpress install it with the help of the system it runs to. Maybe they can find some error log during the installation (not the folder already exist error, but the error before it).
Thanks!