Can't update from OSX 10.9.5 to OSX Yosemite 10.10 I bought my 13 inch non-retina MacBook Pro on December 2013. It's got...

4 GB of 1600 MHz DDR3 SDRAM

500 GB 5400-rpm hard drive

To update to OSX Yosemite 10.10 takes 5.64 GB. So does it mean I CAN'T update from 10.9.5 to 10.10 OSX Yosemite with my MacBook Pro?
I think you are misreading the numbers.

Yosemite takes a little more than 5 Gig.

Your Hard drive is 500 Gig. Even if you have used (consumed) lots of it, if you still have about 10 Gig of free space you can upgrade to Yosemite.

To look how much space you have on your Hard drive: 

Click on the top left Apple symbol and then on the About this Mac.

In the new window click on "More Info", now click on the Storage Tab.

It looks like this on my Mac, showing I have 108 Gig free.



The other storage is called RAM (that is not your hard disk). Yosemite needs minimum 2 Gig and you have 4 Gig, so no problem there.