How Do I Re-size Images Across Entire Site?

My pictures are too large on my site and they look cluttered. I would also like to be able to add more content but the pictures are now taking up too much space. Is there a way to re-size all pictures or edit all pictures at the same time? Thanks in advance for your help.

Just go to settings => thumbnails and resize the images to whatever you want.



brandonvd Thanks. I found thumbnails and there are many options. Which option am I supposed to change? And do the changes take place immediately or will they take some time, because I have about 30,000 products on the site?