You should perform the following steps on a new SD card. Don't mess with existing solutions. It is not worth the $5 to loose something working.
I'm used to use Raspbian, so my suggestion is to go to https://www.raspberrypi.org/downloads/raspbian/ and download the latest Raspbian Stretch Lite. Flash it to your SD card. Mine have usually 16 GB, but maybe smaller work too. I'm using Etcher on macOS, a great tool for flashing.
After successful flashing enable ssh and prepare a running Wifi configuration.
A Wifi adapter should be attached to your Pi of course.