Which program can be used to increase the resolution of an image without losing quality?

I have tried several programs in the last year and I come to the same conclusion that  @daniellei4510Topaz Gigapixel AI gives impressive results. Very effective for photos, illustrations and graphics. I think that for the moment it is the best, it is not free but it is worth the investment.

Gigapixel AI is considered the best. I've successfully upscaled 1024x assets up to 30 inches at 300 dpi on the longest side (though I generally stick to 20 to 24 to make it easier to edit). Gigapixal AI has an upside and downside to it, which cancel each other out. Let me explain: It can often over-sharpen certain areas of an asset (hair and irises, for example). However, in addition to the sharpened layer, it upscales the original layer as well that is far better than what can be accomplished in Photoshop. This layer is a little softer, so that the over-sharpened areas of the top layer can be masked to reveal a softer layer beneath as needed.