Login to your Dolphin 7 Administration.
On the left hand column find and navigate to:
In the center of the page find and locate the "Manage Keys" area.
Find the filter area and enter "welcome to the community" (without quotes) and check the Apply box.
You should see _Welcome_to_the_community (System) with an edit link next to it.
Click on the "edit" link.
A little window or prompt will open.
Change the "String text for English language:" to whatever you want it to say.
In this example I have entered: My Site or Slogan!
Then, just click the "Save" button.
Now just visit your homepage and/or refresh your homepage for the changes to take effect.
Original with Welcome to the community!
After changing it to My Site or Slogan!
If you want to change it just go back to the Dolphin 7 Administration panel and edit the _Welcome_to_the_community (System) key again.
As you can see there's not much to this one and it only takes a few moments to change it.
At the time this Tutorial was posted the current version is: Dolphin 7.0.9
Other related Tutorials:
How to Hide or Remove Welcome to the community
Language Settings Intro