1) Login to your OpenCart admin panel. In your browser address bar type http://yourdomain.com/admin. If you have installed your Opencart under a subfolder “store” for an example the above URL will change to http://yourdomain.com/store/admin. Login using your username and password.
2) Navigate to Catalog > Products
3) Click Edit button next to the product name
4) Select Image tab
5) Click Add Image button
6) Click on Browse Files to upload your image
7) Click Upload to upload images from your computer
8) Select the image on your computer and upload it. Double click on it in the list to select it. Save the changes
Feel free to check the detailed video tutorial below: