You should always resize and optimise your images before uploading to your website or cart. Optimal sizes will vary depending on your design but as a rule images if optimised/resized properly should be no more than 150kb each. This will ensure your pages load at a good speed and also keep you from going over your disk quota.
A good free tool for optimising/resizing images before upload is Cam2PC.
Link here https://www.nabocorp.com/cam2pc/
Note you should optimise AND resize.