downloaded themes

[lock]

I am still having problems with applying downloaded themes from microsoft
office to my presentation. When I apply one downloaded theme to one slide, it
changes all the slides. When I click on apply to selected slide, and then
apply another downloaded theme to the second slide, that slide kicks out the
previous slide and changes not only the second slide but also the first slide
and all of the other slides to that theme. These downloaded themes are not
built in. Does anyone know how to apply downloaded themes to a presentation
using different downloaded themes for each slide? This is very frustrating.
Please help!