Did you try clicking "customize" from your actual member page under your profile image as well as when you 1st log in (I remember there being an option when you 1st log in but I am always logged in so I can't recall for sure)
A drop down menu should show up at the very top of your screen where you can choose different themes, colors, or even upload your own style. Do you possibly have pop up's blocked? If so try adding the site as allowed for pop ups.
If for some reason it still is not working let me know and I will get it reported to tech support for you.