To uninstall Yoxel from Salesforce, go to Salesforce Setup, navigate to Installed Packages section and click Uninstall link next to Yoxel Sync package. This will kick off an uninstall sequence that should uninstall Yoxel.
Note that after you have uninstalled Yoxel it may take several minutes for the Yoxel tabs and package to be completely removed from your Salesforce org.