Simply select the text you need to delete and press the Delete key or the backspace key, or type in the text with which you want to replace the selected text.
In tables you often want to delete text without deleting the cell containing it. However if you select a group of cells and press Delete, both cells and contents are removed. To delete just the text leaving the table intact, select the text and display the Make menu from the Edit menu, and choose Make Blank.
If you only want to remove the content of a single cell, you can use Delete as normal.