When uploading images to your website, always be sure that the file size is not too big. It is the standard that images that are posted on websites should be no larger in file size than 250kb. If you are unable to reduce the file size below 250kb, then it is preferable that the size stays under 850kb.
This size is recommended because each individual has a different internet connection, which will determine how quickly they are able to view your website. Keep in mind, if you upload multiple images that are 500kb-1MB in size on one page, that page could end up having 4-5MB, which causes the visitor to have to wait for an indeterminate amount of time to view that particular page, which they may just not even bother to wait for the page to load.
Remember, it's the file size, not the size/measurement of the image(s).
You want to make sure that you always save your images as JPG files as those tend to be smaller in file size. When saving as a JPG, if given the option, always select "Compression Type: Progressive"
If you have access to it, you can reduce the file size of an image using Adobe Photoshop, but if you don't have the funds for that program, here are few examples of free options online: