diff --git a/tests/external-backend.md b/tests/external-backend.md
index 4b1c0d79f4d..1835bfb1390 100644
--- a/tests/external-backend.md
+++ b/tests/external-backend.md
@@ -10,7 +10,7 @@ $ export SPREAD_EXTERNAL_ADDRESS=<instance_ip>:<instance_port>
 * From the snapd project's root execute the script to setup ssh access to the
 instance:
 ```
-$ ./tests/lib/external/prepare-ssh.sh <instance_ip> <instance_port>
+$ ./tests/lib/external/prepare-ssh.sh <instance_ip> <instance_port> <launchpad_id>
 ```
 The default values for ip and port are `localhost`, `8022`. This script assumes that
 the user created by console-conf has the same name as the user executing the
@@ -18,20 +18,7 @@ script, if that's not the case you can pass the created username as a third argu
 to the script.
 
 * From the snapd project's root execute the suite selecting the type of system of
-the instance, currently `ubuntu-core-16-64`, `ubuntu-core-16-32`, `ubuntu-core-16-arm-32` and `ubuntu-core-16-arm-64` are supported:
+the instance (spread.yaml file lists all supported systems) by executing the command:
 ```
-$ spread -v -reuse external:ubuntu-core-16-64
-```
-* You can execute again the suite by just reissuing the spread command, no need
-to run the prepare script again.
-
-Suppose a new core revision is published and you want to check if the core snap from stable
-can be safely refreshed to this new revision. Then, assuming you have a ubuntu-core instance
-created from the stable channel and the new core has been published to `<core_channel>` you
-can run the `tests/main/core-snap-refresh` like this:
-```
-$ export SPREAD_EXTERNAL_ADDRESS=<instance_ip>:<instance_port>
-$ ./tests/lib/external/prepare-ssh.sh <instance_ip> <instance_port>
-$ export SPREAD_NEW_CORE_CHANNEL=<core_channel>
-$ spread -v -reuse external:ubuntu-core-16-64:tests/main/core-snap-refresh
+$ spread external:ubuntu-core-20-64
 ```