[Nimbus]

If it's saying that the resolution is too low, it means that the quality of the photo is not good enough for the size of print or photo gift. Increasing the resolution of an already existing photo would not increase the quality of the photo. So it would still look poor.

Anyway, what this is (probably) asking for is a larger photo in terms of number of pixels. Instead of a photo that is, say, 640x480 pixels in size it wants a photo that is at least 1080x960 pixels in size (for example). In order to increase the number of pixels, you need to upsample the photo.

You can upsample an image in Photoshop or other professional photo apps. Or you could use an online tool. I just did a very quick google search for "upsample image online" and here's the first one I came across:

imageenlarger/

I have never used the above website so I have no idea how good it is or anything.

As I've already mentioned, upsampling the image won't improve the quality. So it may not look very good when printed onto the photo gift.