The city/highway percentage is made up of all the fuel-ups you've entered so far. So the only way to change what you see is to change your past fuel-up data. (Here's info about editing a Fuel-up:
How do I edit or delete a fuel-up?) It's a bit like changing any statistic on your Fuelly page. If you want your average price/gallon to go down, you need to go back and change the price you paid for fuel-ups. If you misreported the city percentage for various fuel-ups you can go back and change them.
If you start reporting a higher city percentage, the number will change over time.
Another option is to completely remove the city/highway chart from your page. You can do that by
editing your vehicle and selecting No next to the "Track City vs Highway?" option under Reporting Units.
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