Your computer is still bound to your company's local domain? How old school. Well, here's a step-by-step guide how to join Azure Active Directory (AAD Join) with Windows 10.
You must be administrator on your local computer, Your existing use profile (C:\Users\<account name>) will continue to exist, but anyway, it's a good idea to backup your local data if needed. Usually such "local" data should be synchronized to the cloud anyway, so it's easy to restore (for example with OneDrive).
So here's how to join Azure Active Directory with your computer.
Open the Windows 10 Action Center with the notification icon in the bottom right corner near the system tray and click "All settings".
In the "Settings", click "System".
Click the "About" menu. In here, below the Windows 10 logo, click "Connect to work or school".
[If your PC is still connected with a domain, remove that connection in the following settings, restart and continue as described here.]
To join an AAD, click "Connect".
Ensure that "Join this device to Azure Active Directory" is selected.
Now enter your AAD account, as "firstname.lastname@example.org" (your Office 365 User Principal Name, equals your login) and click "Next".
Enter your password, followed by "Sign in".
If you are using Multi Factor Authentication (which is a good idea), confirm the password.
After the successful login, confirm with "Join".
After that, you receive a welcome message, saying that your computer is now connected to the AAD of your organization. Click "Finish".
Back in the System settings, you will see the new "Connected to <our company>" entry.
Restart your computer.
Login with your Office 365 account ("email@example.com") at the Windows 10 login.
If your company has configured Windows Hello, you can also login with a PIN or biometric data.
Don't forget to remove your old user's profile directory if no longer needed. The new user's profile is usually named C:\Users\<username>.<domain> (without the domain extension, for example C:\Users\john.contoso).
Easy going! Now start with a clean profile and configuring your environment.