You can change the permissions for files through the cPanel File Manager or in your preferred FTP program. In File Manager, locate the file you wish to change the permissions for. Next, right click and select Change Permissions from the menu (or select the icon near the top of the screen).
This will bring up the Change Permissions window where you can adjust the settings as needed by checking the box by each permission you want for each level of access (User, Group and World).
Once you are finished editing your file permissions, click the "Change Permissions" button.
Keep in mind that you should only change file permissions if needed. You want to make sure that you aren't allowing more access to your files than is necessary, since that can leave your website vulnerable.
Incorrect file permissions can cause errors or even worse, allow unauthorized users to hack your site. Remember that 777 permissions means that your file is readable, writeable and executable by the "world". This is not common, as it is a rare situation where a file needs to be written and executed by the "world." If you find files or folders with permissions that do not match the default permissons, it's usually best to change them to the recommended permissions.