Sure. Start with these:
You need to log on as either an administrator or a host. There is a "skins" menu entry under both admin and host tabs. Work don under the host tab applies to the entire installation and work done under the admin tab applies only to the particular portal.
I'll assume that you have a .zip file that has the skins and containers.
Select the appropriate "skins" menu entry.
Using the dropdown next to the Skins title (it's the little triangle that points downward), select "Upload Skin". Then, browse to find the zip file and click the link to save. DotNetNuke will process and install all of the skins and containers in the file.