The first link in the Command Bar under "Add/Edit Pages" allows you to change the column widths.
You only have an option for 1, 2, or 3 columns.
You can vary the number of columns and the width of columns within a guide, but each page of a guide can only have a single configuration, i.e., you can't have a page with one wide column stretching across the page with 2 or 3 narrower columns beneath it.
The default setting is 3 columns (narrow, wide, narrow / 230, 520, 209).
"For 3 column layout, enter non-zero numeric values for each column width, in pixels. The sum of all 3 widths has to equal 959. Recommended values are 230, 520, 209."
"For 2 column layout, enter 0 for the left or the right column. The sum of widths for the center and the other non-zero column has to be 967. Recommended values are 0, 758, 209 (for hiding the left column), or 209, 758, 0 (for hiding the right column)."
- For a slightly less narrow left column, enter 300, 667, 0.
For a 1/3 - 2/3 split of the width, enter 322, 645, 0.
For an even split of the width, enter 484, 483, 0.
If you enter 0 for the right column, it will automatically suppress the profile box. If you still want the profile box to appear on the page, but you want it to appear in the left column, you can "Flip Profile Position" even after the right column is no longer being displayed.
"For 1 column layout, please enter 0 for the left column and the right column and 975 for the center column. This will make the center column the only visible column, 975 pixels wide."