To Merge and Unmerge Cells
Merge Cells
You can combine two or more table cells into a single cell. When merging multiple cells, the content of each cell being merged is added on a new line in the merged cell.
1. Use the Ctrl key to select multiple cells that you want to merge. Select the opposite corners of a range of cells to merge across rows and columns.
2. On the Format tab, in Rows & Columns group, click 
Merge Cells. Alternatively, you can click from the mini toolbar that appears upon selection.
Merge Cells. Alternatively, you can click from the mini toolbar that appears upon selection.The selected cells are merged into one cell.
Unmerge Cells
Unmerge replaces the merged cells with the original cell structure. You can unmerge only merged cells, you cannot split an unmerged cell.
1. Select the merged cell you want to unmerge.
2. On the Format tab, in the Rows & Columns group, click 
Unmerge Cells. Alternatively, you can click from the mini toolbar that appears upon selection.
Unmerge Cells. Alternatively, you can click from the mini toolbar that appears upon selection.