Hi Massiv,
currently you can only change the look of your tank with gold.
You can obtain gold by killing marauders, but it doesn't drop that often so will take you a while. But you can also visit the cash shop from within the game and on the shop home page Press the Sponsor Pay tab.
With Sponsor Pay you can obtain gold by clicking on the FREE link and completing surveys, registering on websites or downloading sponsors applications.
If you look through the other Sponsor Pay tabs there may be something that you are genuinely interested in and if so, these ones tend to be worth more gold.
SJ