How to rename the plugin PHP file without affecting existent users?

Depending on the plugin version delete the file init.php on upgrading from the plugin folder. For this purpose you can use the Filesystem API, especially the delete() method – here exemplary linked to the WP_Filesystem_Direct class.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)