Go to...  "Manage Pages" and at the top of the page you will see "Create Individual Member Level Welcome Page Content" - Click that link and you will see all the individual membership level you have created in the system - Click the edit buttons along side the member levels to create the content that will be displayed to the members of this level.

Edit the content as you need and hit submit.

Then to activate it...

Go back to 'Manage Pages'

Open member_panel.php in the editor and insert the [member_level_content]  tag where you want the specific content to display.