You can edit the Important Messages shown on the Login screen very easily: As admin, just edit the records of type System News which are stored in the root folder.
Welcome to TYPO3
Explore the different roles. Login with one of the following usernames and the password that you choose during the installation routine:
- admin = user with full access to the system
- simple_editor = very limited access, ideal for basic editing
- advanced_editor = more power, but still limited to exactly what an editor is supposed to do