When changing the number of columns here are some things to consider:
To change the number of columns for all the pages based on a specific Master Page, you should edit the Master Page itself. So that the changes adjust the text frames (and not just the guides) on your document pages, choose Layout > Layout Adjustment and turn on the Enable Layout Adjustment checkbox.
To change the columns for both left- and right-hand pages of a spread, select both page icons in the Pages palette, otherwise you'll be changing just the left or the right page.
Alternatively, you can change the margins and columns for a range of pages by selecting those pages in your Pages palette.
To reflow your text according to your new column grid, the Layout Adjustment option must be enabled.
Figure 15.8. Layout Adjustment.