Login to your VPS via SSH and run the following commands:
1. Move to the main Multicraft jar folder
2. Download the latest BuildTools jar from Spigot website and remove the old one
3. Run the BuildTools jar and wait about 5-10 minutes for it to complete
java -jar BuildTools.jar
Once its finished it will output a file and say something like “Saved as spigot-1.9.2.jar”
You can now input the name of the spigot file into the “jar file” text box on Multicraft and save/restart your server.