To delete the contents of the current field in a table, first click in the field to select it and then right-click your mouse and select Cut (alternatively press the Del key, click on the Cut button on the toolbar or select Clear from the Edit menu).
To delete the contents of several fields, select the fields and again select Cut, Clear or Del. You can select several fields in several rows by dragging the mouse.
If you used Cut to delete the contents of the field(s), you can of course use Paste to move the contents to another field(s).