Go search google these exact words "GIMP" ha yeah thats all, there should be a website and the download is free and actually the entire program is free but what I recommend is you buy Photoshop or just a Photoshop in general then if you need help I can help you out.
Use gimp if you need something immediately it installs pretty fast, but if you ever used Photoshop you would know both the programs are pretty different.