If a cell contains more text than can be displayed, you can choose to wrap the text within the cell or merge the cell with empty, adjoining cells. Wrap text to make it display on multiple lines of the cell. Merge cells to combine adjoining cells into one larger cell.
If you change your mind, re-click the Wrap Text command to unwrap the text.
If you change your mind, re-click the Merge & Center command to unmerge the cells.
Click the drop-down arrow next to the Merge & Center command on the Home tab. The merge drop-down menu appears.