Resize a Sprite-Texture (editor)

Hi,

we have the following issue. We created our levels and used lots of SpriteRenderer sprites. Most of them we placed on 512x512 textures. Now we decided to rescale them to 1024x1024 to have sharper images on iPad Retina etc.

However, how can we rescale the sprite-textures without re-slicing all sprites again (which would take days)?

Unity can handle the other way around. It's no problem to have a 2048x2048 sprite-texture and reduce it to 1024x1024 for certain devices (Inspector -> Texture -> "override for Web").

Any idea?