You can modify the catalog output in Catalog Settings > Front-end labels. It is the last tab in settings:
When you first navigate to this screen you will see all the available labels for individual product page:
The labels that you can edit by default: product price, free, product shipping, sku, product description, product features, see also different, return to products. When you install any extensions more can come up in the settings.
You can modify any of the labels and save changes. You will see immediate change on all product pages.
Product Listing Labels
If you want to edit labels on product listing please use the menu on the left and switch to listing pages labels:
The labels that you can edit by default: all products, main categories, subcategories, all, products, next page, previous page, home. When you install any extensions more can come up in the settings.