Can I change/upgrade the graphics in my Laptop?

The only things which can be changed in a laptop are
Hard Drive \ Memory \ Cd Drive.
Everything else is soldered together.

DR Tech is not entirely accurate.
The Z510 does have a graphics card NOT motherboard soldered, but instead socketed.
The issues about upgrading graphics in a laptop are:
1) Only when not integrated in the CPU
2) The cards are semi-custom
3) Their drivers are then also semi-custom
4) The cards are not sold in retail outlets. They are spare parts to replace broken ones, and sometimes on ebay or amazon, often salvaged or sold from China factory outlets and repair shops.
5) Warranty voided, and zero support from any laptop brand
6) Can damage a laptop in the disassembly and reassembly
7) The power is designed for a certain range, and cooling also. A higher performance card may cause overheating, or may not get its required power, or could cause a fault as fuse blow.

So, if there are Z510's similar to yours with a higher performance graphics card, in the same family of laptops with common mechanicals and connectors, you could buy it as a spare part. It would not be a GTX 680. The laptop NVidia graphics end with an M for Mobility and are lower performing. The tower graphics cards are physically unable to fit. There are a few laptops with PCI Express slots that can take an external setup graphics card, but they are rare now, and yours is not one of them either.
A GT 740M reports G3D average 878 here:
http://www.videocardbenchmark.net/gpu_list.php
Very slow load, very high data web site page of GPU to gaming in laptops:
http://www.notebookcheck.net/...849.0.html
GT 740M is rank 119 (lower rank is better) and shows expected gaming.
GTX 680M is rank 32 ; G3D score 3526
GTX 680M is a 100 watt GPU, but GT 740M is only 33 watt
First, probably no compatible card. Second, would either overheat or not get the power. Third, who knows what driver would work to run the card, if it exists.
Z510's do come with either i5-4200M. Or i7-4700MQ. If you don't have the i7, and could find one, that is a potential upgrade that helps non-gaming speed.
A detailed model review shows only a GT 740M model. Unless somebody successfully upgraded
From GT 740M score 848, GT 745M score 1145, GT 750M 1500, GT 755M score1687, GTX 770M score 2899, GTX 775M 4530, GTX 780M 4340, GTX 850M 1518, GTX 860M2097, etc
with wattage found on notebookcheck sites, but no way to know what fits and if it works by drivers, it is an expensive guessing game. The GT 750M and GT 755M and GTX 860M have small potentials as also used in Lenovo products and there are existing cards that may or may not work or fit the socket and space.
Few people try unless there was another product with common parts to the laptop.
GT 755M is about 50 watts in a card. There's very little experience, because few people do it with any laptops at all, and you would need someone that did it with a Z510 and found a card.
BTW, LCD screens are sometimes changed. That is a fabulous upgrade in a Y50 laptop going from their standard 1080p to an IPS 1080p.