Changing cams isn't hard. Just unbolt the old ones and bolt in the new ones.
Adjusting the shims so the clearances between the cam lobe and the valve is a hassle. I have never done it myself, but I believe it involves a lot of measure clearance, remove cam, adjust shims, fit cam, repeat. Although I'm sure someone like MrShin, IRA11Y of maybe even Google could enlighten us.