That will still work, however the you won't be able to turn the graphical settings any higher. unless you have GPU with higher memory.
So my brother have the following PC:
AMD Athlon II x2 250 3.0 Ghz
ASUS M4A88T-M
2GB RAM
MSI Radeon R7 260 GDDR5 1GB
Corsair CX430
and I was thinking about upgrading it for about £500 (No OS, mouse, keyboard, monitor, secondary HDD and case as I already have those

Tho 128/250 GB SSD is essential for the system.
so I was thinking about either:
1) upgrading the processor to stronger and better along with 16 GB of Ram
2) Just leave this graphics card and invest into new mobo, maybe put another MSI R7 260 GDDR5 1GB into Crossfire to increase even more power , Ram, power supply and processor.
3) Just buy new build ?
what's the best option here ?
My brother really wants to play the Witcher 3 but I don't know if after I upgrade his computer will be able to be able to pull this game + GTA V and CS Go on higher settings on 21" Monitor ?