I’ve just migrated the blog theme from Sandbox 0.6.1 to 0.9.5. The skin management has been completely overhauled in this version. The XHTML structure has and some classes have been slightly modified, so you’ll need to tweak your current CSS skins. And the skin management option on the admin dashboard is gone, but you can easily bring it back installing the skinner plugin.
In order for the skinner plugin to work, you’ll need to follow the instructions on its page. Namely, you’ll have to create a “skins” folder into the sandbox dir, and then a subfolder for each individual skin, like “sandbox/skins/sandbox-k2”. On that dir you’ll have to put the style.css file for the skin.