Ideally, you'd actually need to upgrade ALL of those - the CPU, motherboard, RAM and GPU and disks - in order to run any 2018+ version of Premiere Pro CC adequately smoothly. That's partly because your i5-4460 (unlike almost all modern multicore CPUs from both Intel and AMD) does not go anywhere above stock clock speed when all four cores are under a full load (or put it this way, the turbo boost self-overclocking feature in the i5-4460 only functions with three or fewer cores in use).
As a result, I would recommend that you not waste another cent on that aging system at this point - not because whether or not its performance can be improved per se, but because there is really no cost-effective upgrade whatsoever for it. In fact, a GTX 1050 Ti, although it would have improved your PC's performance, is still priced too close to that of the much better performing GTX 1060 6 GB for its own good. Instead, save up for an entire new PC. However, if that isn't a feasible option in your foreseeable future, just upgrade the system RAM to 16 GB or 32 GB and fuhgeddaboudit.