Sitecore 9 installation process is quite different than previous version. The new installation process uses, Sitecore Installation Framework (SIF). You can find installation documents in Sitecore 9 release page. The earlier version of Sitecore installation was easy and it was not hard to remove a Sitecore instance from the computer. If you had used SIM, it was even easier, just clicking a button would do it.
After I installed my first Sitecore 9 instance, I realized that, it installed the websites in C:\inetpub\wwwroot and created all the databases in the C drive. My C drive is smaller SSD drive and I don’t install Sitecore instances in it. It is reserved for only OS. I thought, it will be useful, if I create a script to remove the instance and share it with others. Here is the script.
There seems to have some issues with gist rendering in the blog. If the code is not displayed in the blog, this link will directly take you to Github gist.
Final Thoughts: SIF is extensible and it is probably possible to extend it to add the instance removal functionality. I will look into that as time permits. Feel free to change the script for your use. Make sure you run it carefully. Once the instance is deleted, nothing can be recovered.