To replace the WLAN card in an X220, you must remove all the screws on the bottom of the case, the keyboard, and the palm rest. It's not trivial but anyone can do it.
Unfortunately it would be largely pointless since the X220 has an allowlist for PCIe cards, and I'm sure it does not include any modern wifi devices.
I upgraded the WiFi cards in my X200 units by installing Coreboot, which has no PCIe allowlist. https://www.neilvandyke.org/coreboot/ I don't know the state of Coreboot support for X220, and the entire process can be a headache, but it might be an option.
I understand some people instead use modified stock Lenovo BIOS to defeat the PCIe allowlist.
Unfortunately it would be largely pointless since the X220 has an allowlist for PCIe cards, and I'm sure it does not include any modern wifi devices.