If you have made changes you want to keep, Close then Save the file.
Click on the purple R in top left corner, then Close.
Then select Synchronize with central:
The Synchronize with Central dialog box will appear.
Make sure all available tick boxes are ticked under After synchronizing with Central relinquish the following worksets and elements:
Basically you need to give back everything you've taken possession of so others can work on them.
Click OK and you are done.