You can upgrade using steem or wait until you generate enough recourses

Hope the screenshot makes it more clear.

On top you see how much per day. On right top you see small (mobile screenshot) + 1.61 reward that's the steem generate.

I upgraded some buildings with steem. You have office buildings, drugs buildings and weapon buildings. You can train sort of people to defend attacks from people who want to steal your drugs but you can do the same but I'm not that far yet.