I remember asking this question a while back when the new system was implemented, and to put the answer of Jarace in short terms: the “profilelogo_guildname” code now requires you to put the numbers given by the file name at the end of the code. Ex: profilelogo_guildname_(file numbers).jpeg
These numbers are completely random, and are shown with the file name inside the game files. Now, How you plan to obtain your guild logo file is completely your decision. Android users have built in file managers, so if you’re using an idevice it may not be possible (Unless you intend on buying one of those sketchy file managers on the App Store, which I don't really recommended). Hope this helped.