Where is the mac id on a pc and can i change it?

What you're talking about is the Ethernet MAC address (aka physical address), which is assigned by the network card manufacturer & cannot be changed. It looks something like this: A4-BA-DB-F2-59-55. Changing the motherboard will only change the MAC address if the network function is built-in. If you've got an Ethernet network card (PCI) you can replace it w/a different card & that will change your MAC address. Last but not least, some routers provide MAC address spoofing, so that all connections to the router present the same MAC address externally (this is sometimes required by your ISP).

The Mac ID (more usually called the Mac Address) is coded into the network 'card'. Most laptops have the network card integrated into the motherboard so changing the motherboard will change the Mac ID. But some laptops do have a network card that isn't part of the motherboard... so can't say for sure. I've heard of changing the Mac ID, but don't have any expreience with it.

The Mac ID (more usually called the Mac Address) is coded into the network 'card'. Most laptops have the network card integrated into the motherboard so changing the motherboard will change the Mac ID. But some laptops do have a network card that isn't part of the motherboard... so can't say for sure. I've heard of changing the Mac ID, but don't have any expreience with it.