Q: How can I change how many products it should show in “Most popular” block?
A: “Most popular” block is displayed via static block.
First, you should create a separate category (for example, "MostPopular") for this section and add products to it. They must be inactive to be hidden in the main navigation. Please see the following screenshot:
Please remember the ID of this category.
Second, open left_info_block or right_info_block to edit. The code is: