Note : The suggested steps should be carried out during a scheduled maintenance window as user authentication may fail for some users during the process of updating user data in the VIP services. 

The below steps will need to be follow to implement this.

1.   Log in to the VIP Enterprise Gateway configuration console.

2.   Click the User Store tab.

3. Click on Edit for the user store which you want to change.

4. Click on Search Criteria to verify the VIP User Name Attribute

 5.  Before changing sAMAccountName to UPN, you will need to do the run once in LdapSync.

 6.  Once run once is completed, you can change the VIP User Name Attribute from sAMAccountName to userPrincipalName (UPN) as shown below:

    7.  To verify, click on the Test button as seen in above screen shot. It will show the VIP User Name as UPN.

    8.  After changing it to UPN, you will need to do the run once again using LdpaSync.