There are various methods you can use to make worksets editable.
To make worksets editable from the Worksets dialog
When you click OK, ownership information is communicated to the central model and to all local copies of the central model, so that all team members have the current ownership information.
To make worksets editable by selecting an element
In the drawing area, right-click an element, and click Make Worksets Editable.
To make project view worksets editable from the Project Browser
In the Project Browser, right-click a project view, and click Make Workset Editable.
To make a sheet view workset editable
In the Project Browser, right-click a sheet view, and click Make Workset Editable With All Views. The sheet view workset and all the project view worksets that are on the sheet are now editable.
Use the Make Workset Editable option if you only want to make the sheet editable. If you already own the workset, this option is not available.