Deleting has no effect on the trace data that's on the screen. Click Tools on the main menu and then click Delete traces in trace file. The Trace catalog opens with Select as the first column. Check the checkbox in the Select column for each trace record you want to delete. Once you have made your selections, click the OK button to delete those records.
You can also delete trace records one at a time by clicking File in the Trace window and then clicking Load to open the Trace Catalog. Right click on the trace record you want to delete to open a popup menu and click Delete selected record. You can also print and rename traces from this popup menu.