Hi kkodiak -
Welcome to Elvenar!
Like many games, Elvenar too has a research/technology tree. What kind of Elves or Humans would we be without upgrading our cities? Let's not think about that..anyways, most buildings after certain levels will require a higher level of technology to upgrade that particular level. You can find the technology tree in-game by clicking on the open book icon centered at the bottom. You can find a lot of information regarding this in our
wiki.
If you ever have additional questions, please do not hesitate to ask on the forum or submit a support ticket. This community is very good about helping!
All the best to you.