Having trouble upgrading

Hey I am using WP 2.8.4 and am trying to upgrade to 2.9.1 but I get this error and don’t know what to do:

Warning: copy(E:\inetpub\vhosts\chadashchay.com\httpdocs/wp-admin/includes/update-core.php) [function.copy]: failed to open stream: Permission denied in E:\inetpub\vhosts\chadashchay.com\httpdocs\wp-admin\includes\class-wp-filesystem-direct.php on line 131

Could not copy files.

Installation Failed

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Can anyone help me?