Yes. You can change your preset at any time by selecting 'Change theme style' at the bottom of the 'General settings' tab.
How do I access the settings for products/collections/articles/pages?
In the theme editor, you will need to navigate to the page you would like to edit, and then click the 'Product pages', 'Article pages', etc. settings panel.
How can I remove the 'Powered by Shopify' and/or 'Designed by WeTheme'?
If you open 'footer.liquid' in the 'Sections' folder, you will need to find the line containing 'powered_by_link', and modify as needed.
I want all of my product images to be the same size?
Our themes have an 'auto-height' setting which aims to ensure all images are the same height, but we recommend keeping all of your product images in the same aspect ratio. There is a handy video by Shopify here that explains all: https://www.youtube.com/watch?v=oiWFh0xUmw4
How can I show related products?
Our themes have a related products section (on the product pages), but there are also 'Related product' Shopify apps that could also be used. These can be found in the Shopify App store.