Can anyone help if I can upgrade to a new graphics card?

Hello, and thank you for clicking on this link! 

I'm, well, a bit of a potato when it comes to these things so I need some help, Wether it be a tech savvy computer person or a tech savvy dell employe. My current computer is an XPS 8700 (I know, I know "A XPS 8700? Haven't heard that name is years...")(not sure if special edition or not.) with an GTX 750ti currently installed. Now I'm hoping to upgrade to a GTX 960, but I do think I have a power supply good enough (no upgrades to supply, recommened on nvidia website = 400W. Please correct if wrong.) But I dont know if it fits or if the power supply has enough "pins". (Yet again another term I don't understand.)

So once again if anybody can help with my delema I'd greatly apperciate it.

Thanks again,

-Dante the computer potato.