Complete newbie to forum changes help please

hi all I have a few questions before I change the look of our forum. I am completely new to it and dont want to ruin what we have or lose anything hence why I am asking for advice here.

Basically we use a phpBB and we have had the style now for a long time and I would like to change it to some thing wider and more modern. I dont want to lose any of the threads etc I just want to swap it straight over with no problems. Can this be done?

You can search for new skins/them on hitskins.com and directly install it there to your forum, you won't loose posts or any data if you do this.

Thank you!