Grant Author type user to change template

i am managing the blog more that one blogs at a time. every blog only have one author or editor. i just want to give permission to that user that he can change the presentation style or theme of the blog.

and please do a favor for me

tell me the difference between subscriber, editor, author

and give me a link where these things are already described

thanks in advance

regards

—
Haroon Sajjad
PHP Developer
haroon373@gmail.com
http://www.phpmetablog.com