Generally speaking, this is a highly restrictive aspect of owning an AIO compared with a traditional tower desktop. AIOs have much more in common with laptops; both may let you upgrade the memory or storage, at best. For some users, that's enough, but it's still not all that common for these mostly sealed designs. Like with laptops, memory or the SSD may be directly integrated or soldered onto the motherboard, meaning you're stuck with what you have. And CPU and graphics upgrades are a nonstarter.

End-user upgrades are just not a priority with AIO designs. Even if an AIO chassis does open up easily and its components are not soldered down, it's more like upgrading a laptop. An AIO may use mobile SO-DIMM RAM (possible to acquire, but not the same size as desktop RAM), and M.2 SSDs may be size-limited versus the full-size slots on most desktop motherboards.

With a traditional desktop tower, installing a graphics card into a system you originally purchased without one is at least an option (provided it has the space, the slot, and an adequate power supply). You'll never fit one in an AIO's interior, however. If substantial future upgrades are a priority or even a concern, an AIO is not the right pick. Get a tower-style desktop.