You can read all of the details for the MKII's on the UA website, but to answer your question, the updated plug-ins are much improved over the legacy versions. If you have any of the aforementioned plug-in licenses you can upgrade to their respective MKII Collection Bundles for an extra upgrade fee.
Of course, select yes for the free upgrade.
When you register your new UAD-2 into your existing hardware group (where you have the UAD-1), you will be given the opportunity to upgrade any UAD-1 plug-in licenses to UAD-2. Click to expand.Well, congrats on your first UAD-2 card! What took you so long? The legacy versions (right now that is the LA2A, 1176LN, Pultec & Fairchild) are the exact same versions as the previous UAD-1, but ported to UAD-2 (SHARC DSP) and now available as 64bit plug-ins.