How to set Maximum File Size?

Hi,

I have a form for uploading photos.  I would like customers to be able to upload up to 10 unedited digital images to my form.

I had a client contact me because he tried to upload images to the form, but it said that the images were too large.

How many KBs should I set the maximum upload amount for my form?  How can I test if this will work and that I will not run into this problem again in the future?

Also: Once a client fills out the form, the information and images are emailed to me (I do not have dropbox or google docs hooked up). I am unsure if this matters or not.

Thanks!

Phoebe