Changing image resolution

Question

1) problem 1 (down sample with exact factor) other components:

e.g.

I have an image with 304X212 .png and would like to down sample it by half to 152x106 resolution.

2) problem 2 (down sample with no specific factor) for background image:

e.g.

I have an image with 480X320 .png and would like to change its resolution to 568X192.

I have an image with 1024x384 .png and would like to change its resolution to 480x320.

This website provides the same image with different resolution. How do they do it?

The reason to do this is to provide image asset for both the iPad and iPhone. I am not proficient with any image processing software. Just a typical iOS developer starting to develop using spritekit.

Please help. Thank you very much in advance.

Answer 1

Blender managed to solve this problem.

Answer 2

Thats vary simple you can use gimp or Photoshop just google it and just make sure that when you are resigning you do not distort the aspect ratio