There is a sample redesign over on Ecomodder, and you can see that you don't need any great Photoshop skills or anything (although pictures will be accepted). Simply describing the improvements you'd like to include is all that it will take to win. According to Ecomodder, "Submission[s] will be judged on numerous factors including how comprehensive/complete the design/plan is thought out (engine, trans, rolling resistance, aero, paint etc.). [...] The longer and more complete the list of modifications the better. 'Best' submission will be judged by Xfi and any moderators of EcoModder.com that have not officially submitted a design."
The contest runs through the end of February.
[Source: Ecomodder, h/t to B. Jones]