This free online (works within your browser, no plugins or software to download) is fantastic. It's amazing how powerful software is getting that will run exclusively within a browser:

https://pixlr.com/editor/

It is heavily Photoshop-inspired, which is great if you're used to using Photoshop. Pixlr even supports image laters. This is perfect if you need a quick application to resize images or do any adjustments. It's very powerful.

Greg