How can I change an internet image to 300 DPI?

Photoshop experts... help. Collage problems still... I wnt to change the DPI?

• I have created a collage in photoshop. I emailed it to a printshop and they said that the image would not print very well as the examples you have sent are very low quality and would only be able to be printed about 6" wide without pixelating. Ideally we would want the files to be about 300-400 dpi. The collage took a long time to create. Is there a way that i can give the print shop wat they want? Hoping you can help here. I want the collage on my wall at A3 size or maybe slightly larger.

• Answer:

  Open the image in Photoshop and go to image --> image size. In there you will see the size of the frame and on the bottom you'll see "Resolution". Make that number 300 and then hit ok. Save and it's good to go. It will make the file size larger, but not the acual size of the image. The file size will enlarge, but that will only matter in how you are sending it. Most of the time you won't e-mail it, but upload it to their site. Hope this helps.