There are many recipes out there describing how to extend the wifi range with Pringles cans etcetera. I went for a more traditional method when I deciding to improve the signal strength on the first floor in the house. (I have a laptop in the washroom so that one can see when the washing machine (or dryer) is finished.)
I have an old Netgear router with dd-wrt firmware and one can configure it to act as a repeater/bridge. By following these instructions it worked like a charm on first attempt.