Changing from one site in the Site Library to another.

Hello, I was wondering if you could help me with what the best practice may be if I want to try using a different site from the Site Library on my blog than the one that's already installed. I know that it's not recommended to do this unless we're using a clean install of WP, but i'd like to try and experiment with a few other looks to see which one I prefer. For example, if I want to see if Wordsmith may be a better fit, as opposed to Dispatch.

I changed the site on another one my blogs while testing, and it created quite a mess, with old elements remaining behind with some of the new ones and I had a hard time cleaning it up. I used a plug-in called WP Reset to set my blog back to it's default state, but would prefer not to do that this time.

Thanks in advance for any advice on this!