The very generalised nature of your question makes it nigh impossible to give you a definite answer. Anyhow, welcome to RetouchPRO!

if you hang around here awhile you are guaranteed to learn truckloads(and probably get addicted to this site as I have). Back to the point, there are numerous ways and numerous graphics programs out there to acheive what you require,and we are a helpful bunch here so you might end up swamped, so might be best to narrow down the field a bit...what graphics program (if any) do you already have access to? I'd say most of us 'round here use Adobe Photoshop of some flavour or another. Also if you could post the image here that might be helpful too
Here's some info about posting images A browse through the tutorial section
HERE may also be helpful for you.
Cheers,
Littlecoo