Go to "Manage Project" from the main navigation:
Then under the "Properties" tab, click the gear icon on the property that you'd like to change:
Then on the property detail page go to the "Data Sources" tab and click on the Google Analytics gear icon:
Then you'll see a menu pop out from the right where you can modify your Google Analytics settings for this property:
Once you've made your change click "Update" and the insight evaluation will begin on your dashboard (usually takes ~ 60 seconds).
There is no limit on how often you can change this and you are also able to change out between different Google Analytics properties as well (if you want to analyze different accounts).