Follow these steps to have only one profile load when you open your outlook:
1. Close Outlook if its open.
2. Go to control panel and click on Mail
For Windows Vista/7, it's under User Accounts:
3. Click on Show Profiles:
4. Select Always use this profile and select the new profile that you made for Office 365.
5. Click on Apply and then Click Okay.
6. Open Outlook. It will no longer ask you about which profile to use. You are now successfully migrated to the new system!