How Can I Edit The Cars Textures?

Hello. I am new here and i come from Portugal and i need some help. How can i edit the cars textures in order to have non tabacco cars. Is necessary some editor? Can anyone help me? By the away: congratulations for your cars Viper they are just amazing. keep on the good work.

you have to have gpmaster or carsetcreator to make the tex files in to TGA's and then you either need photoshp or paintshop pro to edit the tga's..

Thanks. But now i have another problem. The teams jordan, BAR, ferrari, and mclaren are ok. the non tabacco cars that i have created are great but the renault have a problem.
I export the textures but the car stil have "mild seven". I used the renault R23B of viper. Do you have any idea what is the problem?

maybe viper used different tex file for that particular place where mild seven is written ,