This is a point release upgrade and should not effect you in the ways that upgrading from 6 to 8 would give you.
Just make sure you admin clients and at the same version or higher (saves issues with administration).
The upgrade the admin server first – monkey presses button upgrade ie next next next.
The if you have them SMTP servers this will mean that the MIME used at the gateway is the newest. Then all other servers. Mixed version clusters are OK but it is best practice not to have this for long.