This gets asked fairly often and is actually fairly fast and easy. It gets asked a lot in the Boonex Forums, but I thought I'd write a quick guide up and include some screen shots.
First login to your Dolphin Admin Panel.
On the left column find "Settings" then click on the "Languages Settings" as pictured.
We will search for the term copyright. In the "Search for Strings" Look for box enter copyright and click the search button as pictured.
You should get a few results, In this case we want the _copyright Key. Now click on the "Edit" Link as pictured.
A new window will open up. Now simply change the "String" area to what you want your copyright to say. Be sure "Recompile corresponding language file to apply changes." is checked, then click the "Save Changes" button as pictured.
Now just refresh your web browser to see the changes to the copyright you made.
There are also many Language Keys you can adjust or change the text for in Dolphin using this same concept. Just search the Language Settings. For best results keep the search term/word simple and short. There are some Language Key's that use variations so a little exploring might be necessary. It's pretty easy once you get the hang of it.