If you're the Guild leader you can change your Guild name by contacting support here.
As a Guild leader, you can do many things to manage the Guild, such as recruiting and managing members, setting weekly goals and requirements and encouraging the Guild to participate in events. The one thing you can't change is your Guild name inside the game in Gems of War. This is done by the technical support team so we can ensure your name meets the community guidelines.
How to change your Guild name
Open a support ticket using this form. Include the name you want it to be changed to, and other possible variations in case this name is taken. You must be the Guild Leader to change the name. If your Guild leader is inactive, you can take their place as the next highest ranking member after 21 days and request to change the name. For more information on this see: Guild leader is inactive.
NOTE: We can only change your Guild name once, so choose carefully!