You need to, of course, root your device. Then, you can install something called Xposed. You will have to search to figure the xposed installer out. Xposed has several components that can be added, one of which is the G2 module (there are lots of modules that do different things). The G2 module has options to switch your softkey layout.
Of course a complete tutorial is beyond the scope of this brief response. But it should get you started.
Good luck! (it isn't hard...)