Important notice

In the [YourMagentoDir]/app/design/frontend/default directory should be a folder "SkinName"

Magento Template skin change

How to change the skin around the store

Go to Backend->System->Configuration->Design->Themes Tab and set "Skin (Images / CSS)" fields to SkinName value.

Magento Template skin change
 

How to change the skin in the same category

Go to Backend->Catalog->Manage Categories->YourCategory->Custom Design Tab and select "Custom Design" field to SkinName value.

Magento Template skin change