Have a look here first -
http://office.microsoft.com/en-us/excel/HA010346561033.aspx
You might try the below solution I copied it out of help, but if you open it, and your already the owner (your current user name) - it probably wont work - you could add the subcontainers and objects - see below
To take ownership of a file or folder
Open Windows Explorer, and then locate the file or folder you want to take ownership of.
Right-click the file or folder, click Properties, and then click the Security tab.
Click Advanced, and then click the Owner tab.
Click Edit, and then do one of the following:
To change the owner to a user or group that is not listed, click Other users and groups and, in Enter the object name to select (examples), type the name of the user or group, and then click OK.
To change the owner to a user or group that is listed, in the Change owner to box, click the new owner. (select yourself in other words)
(Optional) To change the owner of all subcontainers and objects within the tree, select the Replace owner on subcontainers and objects check box.
Additional considerations
An administrator can take ownership of any file on the computer.
Assigning ownership of a file or a folder might require you to elevate your permissions by using User Access Control.
To open Windows Explorer, click Start, point to All Programs, click Accessories, and then click Windows Explorer.
You can transfer ownership in two ways:
The current owner can grant the Take Ownership permission to others, allowing those users to take ownership at any time. A user granted the Take Ownership permission can take ownership of the object or assign ownership to any group that the user is a member of.
A user who has the Restore files and directories privilege can double-click Other users and groups and choose any user or group to assign ownership to.
The Everyone group no longer includes the Anonymous Logon group.
