Some of you might have noticed you're unable to update Parallels Tools inside macOS 10.13.x/10.14.x virtual machines (VMs) in Parallels Desktop 17.1.3 which is reflected in the degraded user experience: the resolution of the VMs might be stuck at the value of 1024 x 768, shared folders might not work, and some other issues related to that.
Upgrade to the latest Parallels Desktop build and reinstall Parallels Tools
1. On the top Mac menu click the Parallels icon > Check for updates. Follow on-screen instructions to install the latest build.
2. Once the update is completed, start the virtual machine. Right-click the virtual machine icon in Dock > Actions > Reinstall (Update) Parallels Tools.
3. Follow on-screen instructions to reinstall Parallels Tools. Restart the virtual machine once the procedure is complete.