Hi

Are you using slide masters? If so, highlight the slides you want to follow
a particular master, right click the design/theme (depending on which
version you are now using - not sure why someone told you to upgrade...) and
select 'apply to selected slides'.

If you want more info on masters there is a short training course here (the
training is for 2003 but the basics remain the same - just remember in 2007
you need to change the big mummy slide at the top not the little children
slides below).
Design efficiently with masters:
http://office.microsoft.com/training/training.aspx?AssetID=RC011536491033

Echo has a 2007 specific tutorial here:
http://www.echosvoice.com/2007/editinglayouts.htm

Hopefully that gets you started. Feel free to pop back with more questions
and remember, the more specific you are the easier we find it to answer :-)

Lucy