It is important to always optimize images on your website to make all your pages load as fast as possible. You should never upload HUGE images which are much bigger than the size that will actually be displayed, otherwise, they need to be scaled down to fit on the page, but the full-size image still has to be loaded.
Kopage will automatically resize your images down to a MAX size to help avoid this. You will find this option under the general settings. If you would rather take care of any image resizing yourself and keep the original size, disable this option.
It is also good to compress your images to make them smaller.
When you upload images into your kopage website, you have the option to compress the image to make the file size smaller. This will result in your image and thus the page loading faster.
In order to enable the compress image option above, you first need to signup for a developer API KEY at tinypng. Once you have done this, open the TinyPNG app settings in kopage admin and paste in your API key.