If I download an image from the web that is only 72 dpi, and I need a higher resolution to send to the printer, can I just up the dpi in the image size option, or am I on fools errand here?

You can upsize in the manner you described. HOWEVER, all you are manufacturing extra pixels from those which you have in the original, so the expression "Garbage in = Garbage out" applies. Depending on the size and quality of the orig image, your upsized image may look good or pretty bad. Imperfections (jpeg artifacts etc) will just tend to get amplified.
Regards, Murray

There are plugins which do a great job at increasing resolution. Genuine Fractals is one of the best.

You can also get fair results using bicubic smoother and increasing in 10% increments.

But as noted, GIGO. Don't expect miracles.

Regards,

Michael

Thanks all. Looks like it is going to have to be plan B

I really like Genuine Fractals. It has saved my tush many times.

Alien Skin "Blow Up" does a good job too.

PhotoZoomPro has a lots of functions to enlarge files or try to make an action in PS at image size to set the units to% and input 101 repeat the action till U want

saby