AdamBruv :
Why would it need to be replaced?
Well depending on what you want to do, say gaming, the CPU is not very good, the RAM isn't enough, and to replace both of those you would need to replace the motherboard. At that point you will have replaced 80% of the system, including the GPU, and since the MB is already bare-boned it would be pretty difficult to find a replacement anyways.
But like I said it depends on what you are trying to do.
Say you want to play Battlefield 1. Just a new GPU won't cut it. You need at least a 4th Gen i7, which you can't use with that MB.
Say you want to play a game that requires 8GB of RAM, you still can't unless you upgrade the RAM, which is fairly easy, but then you have to figure out the right voltages and everything for that CPU to get the right RAM.
Besides ALL of that. The 1050 is better than the 750Ti. So unless you are getting this 750 Ti for about $50 US, it isn't worth it.