alright, below is a list of Approximatively the parts you have in your system (base on your descriptions) ignore the brand names not relevant.
CPU: Intel - Core i3-550 3.2GHz Dual-Core Processor
Motherboard: Asus - Maximus III Gene Micro ATX LGA1156 Motherboard
Memory: 4GB (1 x 4GB) DDR3-1333 Memory
Storage: 3TB 3.5" 7200RPM Internal Hard Drive
Video Card: GeForce GTX 750 Ti 2GB Video Card
now , this is a dead end system... but there are things you can do to make it last a little longer.
1. change the cpu on it for an I7-860 on eBay can be found easily for about 50$, i7-870 for 75$ and i7-880 can be found to 80$
(important note, to upgrade top some of theses cpus you need to do a firmware upgrade prior to upgrading to the new cpu as indicated on the web site : https://www.asus.com/Motherboards/MAXIMUS_III_GENE/HelpDesk_CPU/ )
2. upgrade your ram to at least bring it to 8GB, sell your 4Gb on eBay and get this ram that will be faster than what you have :
(https://www.newegg.com/Product/Product.aspx?Item=N82E16820231314&ignorebbr=1&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-PCPartPicker,%20LLC-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID= )
Lastly if you have spare change you could move the Os to a 120GB ssd to speed up things but nominal improvements will be seen.
as for upgrading video card that is a toss up considering the system you have.