This recipe will guide you through the tasks required to upgrade VMM 2008 R2 SP1 to VMM 2012, showcasing the possible options and actions. It will then highlight the upgrade path to VMM 2016 in detail.
Go through the Checking the VMM system requirements and preparing for the upgrade recipe after deciding the upgrade method (in-place upgrade or upgrade to another server), and make sure you've installed all of the prerequisites.
If you're planning an in-place upgrade of VMM 2008 R2 SP1 running on a server with an OS other than the supported version, first upgrade the OS, and then carry out the steps to upgrade to VMM 2012, as described in this recipe.