You may want to clear your cache for different reasons:

To save drive space - This is fine carry on
To fix an issue - Make sure you've tried other other troubleshooting steps first.

If you're sure you need to do this then:

Push Windows Key + R
Type/Copy this %USERPROFILE%\AppData\Local\Temp\Yellow Dog Man Studios\Resonite into the Run box that appears
Press Enter or the Ok button
Select the "Cache" folder
Hold Shift and then press Delete. This will skip the recycle bin as the cache can be quite large and is comprised of temporary files.

Regularly doing this?

You should ideally, NOT be doing this regularly. If it's to save drive space then you may want to consider relocating your Resonite folders. However if its to resolve another issue that regularly occurs, please ask in the discord or open a bug on our issue tracker.