The Light interface you are using does not support adding images to ads. You can switch to the Professional interface, which will retain all your created ads and remaining balance.
To switch to the Professional interface, open the My ads page and click on Go to Professional interface at the bottom of the page. Make sure that Professional is selected in the window that appears and click Start using the service.
In the Professional interface, open the ad group editing page in the Supplements block, choose Images → Add.
You cannot add images if you are accessing Yandex.Direct from a mobile device. Please add images from your desktop or laptop computer.
Please describe in detail the difficulties you encountered while adding images. If possible, please attach a screenshot.