FTP details are requested when installing the theme/plugin.

The issue is connected with file permissions/ownership. 

Please edit wp-config.php file and add the following lines:

define('FS_METHOD', 'direct');
define('FS_CHMOD_DIR', 0770);
define('FS_CHMOD_FILE', 0660);

The screenshot shows where exactly it should be placed in the file: http://prntscr.com/ghshy3

In case you still have issues, please provide me with your Wordpress username/password and FTP details in the support ticket. 

Thank you!