There are so many ways of printing posters, just choose the one that you deem is much easier for you.
Using Photoshop
The steps involved are quite simple to follow and anybody can do it. The first thing to do is to find and then open the Adobe Photoshop application. Then Open from the file menu. Choose your file and then click Open. If ever you want to resize your image, bear in mind that any changes made in the physical size of your image will have a direct effect on its file size. The larger the physical size, the larger the file size and a large file size takes quite a while to process. What you can do is to print at a resolution of 150 dpi. The reason for this is that, even if you choose a much higher resolution it will only be deemed useless since additional data from a higher resolution is usually ignored by the printer. Then dont forget to use RGB color mode. If youre already satisfied with the size of your image then you may save your file.
To save your file you have to choose Save As from the file menu in which a dialog box will appear prompting you to type a descriptive name for your file. Be sure to select Photoshop EPS as your format however...