There are not many good ways of separating stamps that are stuck together. One way is to put them into the freezer for a few hours and then carefully try to pull them apart.
Another way is to soak them apart. Use warm water and soak a few stamps at a time. Let the stamps soak for ten to fifteen minutes. Then very carefully pull them apart. The stamps can be put down on colorless blotters to remain until they are nearly dry. When fully dry they can be drawn with a sharp bend across a smooth edge such as a ruler.
A third option is to use what is known as a stamp sweat box. Here is a link to a page that give excellent directions with pictures on how to build oneBellaOnline ALERT: Raw URLs are not allowed in these forums for security reasons. Please use UBB code. If you don't know how to do UBB code just post here for help - we will help out!