The process depends on the game you are playing.
For Goodgame Empire (browser version)
Changing your nickname
Go to Settings (in the top-right corner of the game).
Open the Account Management tab.
Next to your current nickname, click the Pen icon (Edit).
Enter your new nickname in the field provided.
Please note that changing your nickname costs rubies. The required amount will be displayed during the process.
Changing the name of a castle or outpost
Log in to the castle or outpost whose name you want to change.
Click the Paper icon.
Open the Throne icon (Management).
Click the Rename icon next to the castle name (paper with ink and feather).
Enter the new castle name.
Please note that renaming a castle or outpost also costs rubies.
For Empire: Four Kingdoms (mobile version)
Changing your nickname
Open the Settings menu.
Next to your nickname, tap the Pen icon (Edit).
Enter your new nickname in the field provided.
Please note that changing your nickname costs rubies, and the required amount will be shown during the process.
Changing the name of a castle or outpost
Go to the Administration tab.
Select Economy.
Tap the Throne icon.
Next to the castle name, tap the Rename icon (paper with ink and feather).
Enter the new name for your castle.
As with nicknames, renaming a castle or outpost also costs rubies.