Can There Be A Graphics Upgrade?

The simplest thing you can do is to replace the motherboard with a newer one from the same N551 series model. Asus N551VW can generally be considered a good option for such an upgrade:

• motherboard is exactly of the same shape (consider replacing the cooling system)
• all I / O ports and connectors are located in the same places (keep your old chassis)
• it is equipped with a newer (6th gen) Intel processor (VS the currently installed 4th gen)
• GTX 960M graphics has a higher memory bandwith (VS the currently installed GTX 845M)
• total costs make not more than £300 (new MB with i7-6700HQ from China on eBay), and can be decreased by selling the old MB, for example

So, there are possibilities for improvements, but it all depends on how far you want to go with this.