Here’s a crude technique you can use to convert your workset enabled central files back into a single user file. There is (to my knowledge) no official method of removing the worksets from a model but this method may be useful depending on what you want to do with the model.
Start by creating a completely new project. Don’t use a template, create a new project using the dropdown from the 'R' Icon and at the dialogue box choose No template. This means you will get a completely empty project.
Link the Central file into a new empty project using Insert > Link Revit. After loading, select the linked model and then choose Bind Link from the context tab on the ribbon.
When prompted, select Attached Details, Levels & Grids to bring across into the new model (if required).
When Revit binds the link it converts it into a Revit Group. Select the group and choose Ungroup from the Ribbon menu.
You now have a version of your model without worksets! This is also useful if you want to send your model without any drawing sheets etc. It keeps the file size down and allows you to share only the model data.
Note: Something a lot of people don’t realise is that you can also un-bind a bound model and convert it back into a link again. Before Ungrouping, pick the grouped modeled you will notice an Un-bind icon on the ribbon.
This isn’t a fool proof method of converting back to a single user file but it is useful for sending models out to teams who don’t use or understand worksets and central files. One of the down sides to this is that all your views and sheets are not brought over in the process (although this could also be seen as a positive).