I have an image that has been scanned from a 35mm slide. It is a tiff file and is 2.04 cm by 3.35cm with a resolution of 9600. I need to create an image that will go on a wall and be 8 metres wide. Can I do this with this image and if so, how??
What do you mean by "a resolution of 9600"? Do you mean DPI? If so than the pixel width of the file is (9600/2.54) x 3.35 = 12661px
Un-scaled, and printed at 8m wide, this equates to aprox 40DPI ((12661/800) x 2.54)
Which would be perfectly acceptable as a print at this size.
Obviously you wont be printing this yourself at home, let your printer deal with the file & scaling etc.
In Photoshop click Image > Image Size
This is what you will see
Make sure "Resample" is unchecked, and enter 800 as the width. Click OK.
Alternatively do nothing, and tell the person producing the print what size it should be. Technically, you don't need to do anything. Changing the dpi without resampling actually does nothing to the image file anyway, except change the print size, and print resolution.