When selecting all nodes and you are unable to change the polling method, there is an option to group the selection by WMI and selecting only the WMI nodes and then changing the credentials.
All NPM versions
1. Go to Admin > Settings > Manage Nodes.
2. Set the Group By: to "Polling Method". The reason we group it this way is because you cannot change multiple WMI credentials at the same time when ICMP and SNMP nodes are selected as well.
3. Select the check box next to "Name" to highlight all the nodes at once and then select Edit Properties.
4. Verify that all of the nodes selected are what you require.
5. Scroll down and select the "Polling Method" check box to enable you to change credentials.
6. Change the credential to your newly created credential.
7. Click Submit.