docker-compose down needed to enable IPv6

docs/install-update.md

@@ -55,6 +55,12 @@ docker rm $(docker ps -a -q)
 
 ### Step 2
 
+When upgrading from a version older than May 13th, 2017 to a version released after that date, you need to run the following command first as network settings have been changes:
+
+```
+docker-compose down
+```
+
 Pull new images (if any) and recreate changed containers:
 
 ```