Really does look like the server is the owner, not you. So you need more permissions.
Do not know Centos, but think you need to use chown.
As for a download (plu or theme) transport would be like download a zip, extract, put in place; note : there are but few that actualy install, mostly that part (install) has to be doen manually. The downloaded file itself should be at the right section... (sometimes refresh).
(just as comment/throwing it in: out of post read : using private system ? mounted drives> ntfs can cause troubles)