1. Open System Preferences, and select Internet Accounts
2. Select your existing Exchange account in the left pane, and then select the "-" minus button to remove the account.
3. Select "OK" to remove the account
4. Select Exchange as your new account type
5. Enter your name, email address, and password. Click next to continue.
6. Click Continue.
7. Select the data that you want to sync, then click done to complete the process.