First open your admin panel, go to Design
→ Themes → click on the name of your current theme. In General Settings
there are three closed sub categories, click on “Product Listing” it
should show you additional options. The second option there is “Number
Of Rows:”, this value controls the number of rows displayed per page.
The number of products that fit in a row depends on your current theme,
you can change the width of your page or columns. You can do that in
Design → Theme → select your current theme → go to the styles tab. The
space in the middle is calculated from your “Main Table Width” minus
your “Left Column Width” and your “Right Column Width”.
