Select the column you want to resize
Hover over the right edge of the column header until the double-headed arrow appears
Click and drag the boundary left or right to adjust the width
Double-click the boundary to auto-fit the column to the contents
Right-click the column header and choose Column Width
Enter a specific width value and click OK
Use the Home tab, then Format, then Column Width
Drag the boundary between two column headers to resize one or more selected columns
Select multiple columns first if you want them all to have the same width
Use AutoFit Column Width from the Format menu to fit the widest cell content