Hi Pompeius,
With many laptops, the graphics module is integrated (built-in) on the main system board and is therefore NOT replaceable. Although it is certainly possible to upgrade the graphics module in SOME laptops, it is not something that I would recommend. For a start off, the procedure is not like a standard tower system where you can take the side panel off, unscrew the relevant bracket, disconnect a couple of cables and slide the old card out, the replacement being carried out in reverse and taking no more than 10-15 minutes for the complete job. With a laptop you need access to the maintenance and service manual for details on how to disassemble it as you will probably need to strip it right down in order to gain access to the graphics module. This in itself can take upwards of an hour. Even if you can gain access, it is unlikely that you will be able to upgrade the module to one of a higher specification as the components in a laptop are very tightly packed and power consumption together with heat generation and dissipation are major manufacturing concerns. After replacing the card, you will need to reassemble the laptop by carefully following the instructions in the manual. Be aware that any mistakes during the disassembly and/or reassembly procedures can leave you with a totally dead system. If you intend to carry out this procedure, I would entrust your laptop to someone who has experience in carrying out this kind of work, or, if you are very careful, you could do it yourself. Either way, you PROCEED AT YOUR OWN RISK.