As a professional Website Designer, I get this question from clients all the time:
Do I need to resize my images for my website?
For websites including Wix websites, I recommend down-sizing your images to 1980 pixels wide by whatever height they are. This will allow you to use the images full screen without loss of resolution, but they're also small enough that they won't be huge file downloads. Save them in JPG format around 70-80 quality for the best size for web use.
Since not all of my clients have (or know how to use) Photoshop (which is what I use for photo resizing and photoshopping images), you can also use any image editor to size your images to the 1980 pixel size. Here is a handy free image resizer, too, that works great on the fly:
This tool has lots of features like resizing, rotating, saving out different formats, cropping, and more. Totally free to use, too, and much easier to figure out quickly than image editors like Photoshop. See screenshot below: