UEFI BIOS Windows 7 do I have it??

Thanks everybody for your replies! You guys are very knowledgeable, that's for sure. I am a complete novice when it comes to this sort of stuff & I wouldn't be interested in messing around with it myself--I have a wonderful computer guy who does that for a very reasonable price--but I just needed to know whether or not the 4tb hard drive would be a possibility. So my takeaway is that yes, my computer can be set to UEFi, but it is not installed or set to UEFI, & in order to set my system to UEFI I would need to have it installed, format the hard drive to GPT & reinstall the OS, correct?
Sounds like a plan LOL. It is something I am considering for the not-too-far-off-future, I plan to have this computer for a very long time & the new hard drive would be a nice upgrade. I'm not totally understanding why it wouldn't be set to UEFI in the first place, but whatever, just glad it's possible.
Thanks again for all the replies, I learned a lot.