Hi Dec, I am way behind on my emails so I just saw this. I can also see that you have already got a new theme and it's much better than the old one. The navigation problems I had on your site is now solved and everything looks good. Always wise to have a theme with a blogroll. Well done :-)

I have changed themes several times on different websites where I already had content. Yes it can sometimes mess with the way your content is displayed but in my experience it has never caused such a huge issue. Normally you can just change themes without anything major occurring. It depends on the theme that you choose as to how it will effect the content and the layout. When I am creating a new website I like to create a few pages of content first before deciding what theme is best suited to it.

I don't think you will have any major problems in changing theme, but if you do, you could always just change back. Your content wont be erased. You may have to move things around a bit or tweak content to fit with your new theme.

You could always contact technical support too if you are really worried to make sure that there is a backup version of your site that you can revert back to if all goes totally wrong.

Hope that helps.