before you even think of changing the picture you at the very least need to make a copy of it in case you **** it up.
Either make a regular copy or in Photoshop make a duplicate of the picture as a layer and work on the duplicate.
if you use the layers method then your editing will be non-destructive, as it alwaysshould be.
Always save your edited pics with the layers, so you can always change it again easily at a later date if needed.
The clone tool is one method but depending on the background cutting and pasting might also be an option.
There are numerous ways that Photoshop can help you out but without seeing the pic its very difficult to give precise help