Downgrading the macOS is a chore that involves completely erasing the drive and all contents, reinstalling the OS and then restoring all your data from a backup drive. Better and easier to familiarize yourself with the new upgrade and work out any kinks that have popped up.
What macOS version did you upgrade from?
What macOS version is running now?
You can find the current version by clicking the Apple menu () at the top-left of your screen and then select About This Mac. (Note- for privacy and security reasons, please never post your serial number.)
You wrote: "...everything on my mac changed to small..."
This is probably a screen resolution issue. You can fix that by going to System Settings... > Displays and selecting a lower resolution. Choose from the options displayed at the top of that window.
Website access can also be addressed, but we'll need to know what happens when you try to access the sites you want to visit. Do you get some error code or message? Is the problem related to your password? Please give us some specifics so we can help you best. Details matter.