For GPUs, there are two ways it would be (sort of) incompatible.
First, the power supply may not have enough GPU/EPS cables to properly connect the GPU. If that happens, you'll need to upgrade the PSU. With an OEM computer like that, you should see if it uses a standard ATX power supply first, as some OEM computers use proprietary connectors. If it does, it will be very difficult or perhaps impossible to find a suitable upgrade.
Second, the GPU currently in the unit may be a different brand. This is a minor issue. If it does, then you'll need to go through and uninstall the GPU drivers before swapping in the new GPU. Once the new GPU is in, you can install the correct drivers for it.