Permission denied

When I try to upload files I get this error-message: Permission denied
Even though I'm the owner. (This is my homepage).
I never had this problem before.
But some days ago I noticed (when I read the DirInfo) that the user and group name were changed. So when I'm writing to my files (from the net, ex. guestbook) I'm no longer the same user as before.
(When I try to use a FTP-program to upload the files I get the error-message: Not owner.
Sorry my bad English, hope anyone understands...

Waiting for answer/help.

When the user/owner of the files has changed and you were owner before, I suppose that you are not owner any more, despite the fact it is your homepage. You should contact your server administrator.