The welcome page settings can be found in the sidebar, under "Miscellaneous", here:
This screen will present you with the following options:
Enabled
You can choose whether to enable or disable the Welcome page from here by checking the checkbox.
Message Text
You can change the text of the message that appears on the screen here. By using HTML encoding, you can also include links and other content.
Confirm Button Text
You also have the option to change the text that appears on the button that you must press in order to proceed to the assessment.