Migrating sharepoint 2007 themes to 2010

Hi

we are migrating sharepoint 2007 to 2010. Existing 2007 has few custom themes. We want to know how to migrate themes from 2007 to 2010? The issue is 2007 & 2010 theme both are different. We want to know the proper way of migration. Can any body helpus?

Vairavan