Site crashed after theme upload

You probably have either FTP or else file manager access via your control panel. Ask your host for help to access one of those two then rename that theme’s directory to kill the theme. WordPress should default back to the previous theme if it can.

If you have cPanel login just rename the theme folder that you have activated. Solved the problem

• This reply was modified 5 years, 3 months ago by Rams07.

Or check this article

https://www.wpbeginner.com/beginners-guide/how-to-properly-change-a-wordpress-theme/