Probably the "safest" way to change colors would be to click Image > Adjustments > Hue/Saturation. Using the Hue control, you can shift ALL colors in your image. Saturation and Lightness allow you to fine-tune a little. I would recommend you select those portions of the image you want to change and use this tool on them.
There are other, more powerful tools to do this, but if you're unfamiliar with Photoshop, this method is least likely to give you CrAZy results. Match Color and Replace Color are WAY more powerful, but also, will probably require a lot more time from you to figure out.