Can I only profit when prices are going up?

No. One of the major benefits of investing in CFDs rather than commodities or stocks is that you can profit from both rising and declining markets. Remember that a CFD is a Contract For Difference, which means that the difference can go either way. So, depending on what you think will happen, you can invest in the chance of prices rising (a "buy" or "long" order) or falling (a "sell" or "short" order).