You need to refresh the service instance first to make K2 aware of the changes to the list. 

You can do that by either Refreshing the Service Instance for your particular SharePoint site using the SmartObject Tester Tool .  (I prefer to use this method since I find this tool the most convient and powerful)

Or

You can also do it from SharePoint by going to K2 Site Settings, SmartObject Site lists and libraries, and checking the "Do not generate SmartObjects...".  This will refresh the service instance and get the new or modified columns and remove the removed columns.

Then after refreshing the service instance you'll need to step through your SmartObject and select the service instance method and it'll bring in the new properties so that you can map or remove them as appropriate with the SmartObject.  Then deploy the changed SmartObject.

I'll try this the next time I change a SmartObject enabled list.

This time around, I manually updated an exported *.sodx file and published that back to the K2 server.

Hi Tim

We don't have K2 integration component installed on on Sharepoint servers, how can we update a smartobject definition when sharepoint list changes? can we update smartobject using the SmartObject Tester Tool or via other means?

Thanks

Richard

So did you use the SharePoint Content Service object to create the SmartObject?  If that's the case you can refresh the SharePoint Content Service object for that site to get the new SharePoint list changes.

Thanks Tim, I finally worked out how to do it via the Tester tool, refreshing Service Object is intuitive, but it took me a while to figure out how to update the smartobject definition.

So you said it was intuitive, but I can't figure it out? 

Smartobject Service Tester Tool is usually located at C:Program Files(x86)K2 blackpearlBin