Install the latest content manager from https://acstuff.ru/app/latest.zip

If the link above does not work, scroll to the bottom of this website: https://assettocorsa.club/content-manager.html

Unzip the download

Copy the Content Manager file to your Assetto Corsa folder in steam.  The default folder should be something like C:\Program Files\Steam\steamapps\common\assettocorsa unless you’ve moved it (like me) in which case use your correct folder.  The example below shows my Steam folder location which is on D:\Steam\steamapps\common\assettocorsa

Rename your AssettoCorsa.exe file to something like OLDAssettoCorsa.exe (so that if anything goes wrong or you want to change back to the old interface you can simply rename it back to AssettoCorsa.exe and use the old system again)

Then rename Content Manager to AssettoCorsa

You should now have something like this:

Congratulations, you’ve now installed Content Manager.  Now when you start steam, it will start Content Manger.  Everything you used to do in the main menu in AC you will now do in Content Manager – including setting and calibrating all controllers/buttons as well as changing the video modes (rift or screen) etc.

On your first start, you’ll be asked to install a bunch of plugins – just click yes/install on each and every one of them that you can.  They don’t take long, won’t take up much space, and may be used in the future.