How to change flags?

It is possible to use your own images as flags. You have to use PNG or JPG files and name them with the WordPress locale. For example, en_GB.png. Then upload this file in the /wp-content/polylang/ directory (create the directory if it does not exist). Don’t use the /polylang/flags/ directory as your file would be removed when automatically updating the plugin.

Once the custom flag is uploaded, go in Languages > Settings > URL modifications module then click on save changes. Note that your custom flags are not used on admin side.

I’ve uploaded an en_GB.png file to the polylang folder, I clicked on the save changes under the url modifications menu but nothing happened. I should make anything else to assign my image to the English flag? (I haven’t found my image in the list of the flags)