You do not have to uninstall the 2018 TurboTax software. You can have TurboTax for multiple years installed on the same computer.
You do have to install the 2017 TurboTax software, and install the state software, before you can open your *.tax2017 file. After you install the 2017 software, start a dummy tax return to allow you to download and install the state.
