Select line item from tree and modify in targeting panel.
Conditional expressions may be edited in place or with popup expression editor.
Upload changes to DFP. Note that post-load changes made by other means (Web UI or separate SWMF instance) will be overwritten. Perform a 'Refresh' prior to uploading in order to merge changes.
Note also that only active line items can be modified. Such items can be identified by clicking the 'Delivering' links in web UI.