You can replace the GPU on the system board. to do so it would involve removing the system board, shipping it to a board remanufacturer, about $100 (usd) plus the cost of the chip (perhaps $100 or more), then return shipping.
However the extreme temperatures involved in this type of repairs can easily damage the board, so a good used board with the updated GPU would be a more reliable option, as well as costing a lot less and of course it would be an immediate fix. If you sent your board off to get rechipped, then got it back and it didn't work, then you have more shipping, RMA forms, etc... so the only time I'd recommend having a board rechipped is if you have a model that is unavaiable with the updated gpu, such as the 4:3 ratio models where your only hope of an updated gpu is to get one installed, or find a board that was already rechipped.
If you were thinking that it's an easier job to replace the chip then to replace the board, then you couldn't be more wrong.