It's not as simple in laptops as in desktop systems. In short: you will have to phone in your maker’s customer service and find a good tech support person who can look up boards compatible with your laptop model.
Even though the graphics card might be the same, a GF board from Dell may turn out completely different from a GF board on Asus. There are a few problems when trying to upgrade or change GPUs on laptops, and not a main one. First, your board has to be the same form factor. In laptops layouts change all the time as makers try to reduce size and mass, cram more components in, change the heatsink shape/position a bit to better the air flow. Then there is the problem of the interfaces. There is no guarantee that one maker’s connector would be the same as another’s. Some opt in to separate power lines from the data lines, others use single cable for all of that. Connection to mobo will vary at least in position, but may be of a different kind altogether. So really dedicated laptop GPUs are peculiar to the particular model line and sometimes a particular model. If you are able to do “customization” for your laptop on the maker’s site, and it lets you choose a GPU, then chances are there are a few GPUs lying around in their warehouses. If not, you may be lucky in that a “powered-up” model in the same laptop lineup will offer a better card and it may happen to be compatible with them “junior” models. In a case of really good luck, the next generation of these laptops will use the same structure and interfaces for GPU as yours and you will be able to upgrade. So when you are shopping for a laptop you should expect that the only upgradable things on it may turn out to be mem, CPU, HDD, and wifi. Sometimes you will not be able to even use the same size screen from the next gen of the lineup.
Source of information: replaced a few fried-up GPUs on laptops, once with a successful upgrade.
