How to delete iOS runtime?

If you can not find the folder that @Majster mentioned, it's likely because you are looking at Library/ in your user folder.

1) Open a terminal cmd+space and type terminal.

2) Copy-Paste this command into terminal: open /Library/Developer/CoreSimulator/Profiles/Runtimes

This will open the correct folder where your simulators are.

3) Delete the simulators you don't want

4) Restart xcode.

You can find them in:

/Library/Developer/CoreSimulator/Profiles/Runtimes

Also restart Xcode when removing.