SharePoint Enterprise to Standard Edition Downgrade
You can downgrade your Enterprise installation of SharePoint by deactivating and uninstalling some features. Replace the http://url with the correct url.
stsadm -o deactivatefeature -force -url http://url -name PremiumSite
stsadm -o deactivatefeature -force -url http://url -name BizAppsSiteTemplates
stsadm -o deactivatefeature -force -url http://url -name BizAppsCTypes
stsadm -o deactivatefeature -force -url http://url -name IPFSSiteFeatures
stsadm -o deactivatefeature -force -url http://url -name BizAppsFields
stsadm -o deactivatefeature -force -url http://url -name ExcelServerSite
stsadm -o deactivatefeature -force -url http://url -name BizAppsListTemplates
stsadm -o deactivatefeature -force -url http://url -name PremiumWeb
stsadm -o deactivatefeature -force -url http://url -name ReportListTemplate
stsadm -o deactivatefeature -force -url http://url -name DataConnectionLibrary
stsadm -o deactivatefeature -force -url http://url -name IPFSWebFeatures
stsadm -o uninstallfeature -force -name PremiumSite
stsadm -o uninstallfeature -force -name BizAppsSiteTemplates
stsadm -o uninstallfeature -force -name BizAppsCTypes
stsadm -o uninstallfeature -force -name IPFSSiteFeatures
stsadm -o uninstallfeature -force -name BizAppsFields
stsadm -o uninstallfeature -force -name ExcelServerSite
stsadm -o uninstallfeature -force -name BizAppsListTemplates
stsadm -o uninstallfeature -force -name PremiumWeb
stsadm -o uninstallfeature -force -name ReportListTemplate
stsadm -o uninstallfeature -force -name DataConnectionLibrary
stsadm -o uninstallfeature -force -name IPFSWebFeatures