Make sure you claim your home and update your home's info on Zillow with your current renovations. That should help. Also, take a close look at the homes that they are using as comps to value your home. Perhaps the similar nearby homes are in a different school district or there is some other factor that values them higher? In the long run, the comps that value your home along with the updated info you provide should cause the Zestimate to be adjusted higher.