No such thing as a dual core Pentium D, don't be scammed by it. They say its a dual core but it really isn't. I have a friend working for Intel and also have many university teachers, because I study computers at university.
Pentium D's are not true dual core CPU's. My best advice is if you want to, you can upgrade but if I was you I would just keep it and save for another computer and go for an Intel core i3 or even a cheap 1155 socket dual core.
Atleast 1155 will be around for sometime, and you will have the option to upgrade.