How can I view my screenshots from Team Fortress 2?

Question

And do I need any particular software to edit them?

Answer 1

In the directory where you installed Team Fortress 2. It may have its own directory. For some, it is C:/Program Files/Steam/Graphics/

Go there and double click one. Your computer should show it to you if it has a program assigned as a default for that file type.

In that program, whatever it is, you can often "save as" to change it to another format.

The paint program that came with your computer might be good enough. If not then there are free paint progams you can download