1. 	Click the symbol you want to edit, or enter the symbol name. Typing a space brings up a selection dialog with all symbols listed.
2.    A new drawing window will be opened which contains the symbol elements. You can now edit the symbol normally. When you close the window you will be asked if you want to incorporate the symbol into the drawing.
Note: 
When editing symbols, the group and layer functions are not available. The symbol contents are temporarily assigned to group 1 in order that edit/transformation operations can be applied to the whole symbol.