Before you delete, Go to "Control: Database Wizard" and ensure "Compress Before Backup" is checked so the space occupied by the data of these deleted symbols will be recovered next backup and upon each backup.

TO DELETE JUST ONE SYMBOL AT A TIME open a quote page (Click Quote Page | System Quote Page | All Symbols) and right click the symbol you want to delete.  A menu will pop up and choose Delete.  Alternatively, click the symbol so it is the active instrument highlighted and click the red trash can on the tool quote page toolbar.  If you can't see the toolbar, hit CTRL+T to toggle the toolbars or right click and select "Toolbar On/Off". 

TO DELETE ALL THE SYMBOLS AT ONCE open the ".All Symbols" quote page (system quote page), and then click the red trash can button on the quote page toolbar. Click the "+" sign in the upper left corner of the Quote Page and select Show Toolbar. You must make sure that you don't have any specific symbol selected (ie. The cursor is not placed in any specific ticker symbol cell.) To make sure focus is removed from any specific symbol, just click on the "Ticker" column heading (this will cause a sort...but will also remove any specific focus.) If you have a specific symbols selected when clicking the red trash can, then only that symbol will be deleted.

NOTE: If you only want to remove certain symbols and not all symbols, either choose the Quote Page that lists the symbols you want to remove and follow the instuctions above OR right click on the individual symbols on a Quote Page and select Delete.  This will delete the symbol from the Quote Page and remove it from the system permanently.  Just clicking a symbol and hitting delete does NOT remove it from the system, but rather just the Quote Page.

HOW TO DELETE A SYMBOL FROM A CHART
To delete an instrument or pane from a chart click the little "x" in the upper left corner of the chart pane that it is in. If chart pane titles are not visible right click the chart and select "Show Pane Title".