How do you adjust the resolution on a picture already taken?

I am trying to buy birth announcements online, but they are telling me that the resolution is too low and I need to adjust it then upload it again? Is that even possible w/o Photoshop? How do you adjust the resolution on a picture already taken?yeah, photoshop,

change your image size to around 200dpi in image then size.

then go file save for web, adjust the size to around 35k, you do this with the toolbox on your right hand side where it says jpeg lo-high,



35k is usually standard for web.How do you adjust the resolution on a picture already taken?there are much simpler and free image editors. search in www.softpedia.com