You can just add an install package to the group.
Open SEPM
Go to Clients page
Select the Group you want to upgrade
Go to the Install Packages tab
Add a Client Install Package
On the General tab, select the bit (32 or 64). If you have both 32 and 64 you will need to add both packages.
Uncheck "maintain exsiting client features when updating" and select which you want to use.
You can also set an upgrade schedule and over how many days.
Auto Upgrade for Individual Groups