If you need to access your website files you usually have the choice of using a webinterface from your website host or use FTP.
Using a webinterface is generally much faster and easier, but this is not always an option as not all webhosts offer this option.
The alternative is to use FTP which allows you to access the files making up your website. You can delete, edit or rename files.
To do that you will need a FTP program, fortunately there are many around both free and good.
Wordpress.org has a good guide – https://wordpress.org/documentation/article/ftp-clients/ and there is a good one here on wplift.com also: https://wplift.com/wordpress-ftp-access-guide