To change permissions you need any photo editor that can be Paint.NET, Adobe Photoshop, Ulead Photoimpacht, ACD SeeSystem and many others. The most accessible of them, free and not inferior in functionality – Paint.NET. The program has a completely Russian interface and understandable even to a beginner. Download the installation file at:
After installing and running the program, open the desired picture in the menu "File" – "Open". To change the resolution, go to the menu "Image" – "resize". In the window that appears, select "Percentage" if you want to reduce the photo by a specific percentage, or Absolute sizing if you want to get the desired resolution. Below the picture is not stretched and not compressed, check the box for the option "Maintain aspect ratio" and enter the desired width or height of the image in pixels, it is necessary to change only a single numeric parameter, the second will change automatically in accordance with the scale of the pictures.
A few words about saving photos with a new resolution. If you need to maintain the primary photo, not overwriting it, click "File" – "Save as" and save the resulting picture with the new resolution in the desired format in any folder on the computer. Ate the original photo is no longer needed, simply save a photo modified with permission by clicking "File" – "Save".