If you need to create a new Segment that is similar to an existing Segment, click on the existing Segment and then click the copy button on the top right hand side that looks like this: .
Once you click the button, you'll be asked to rename the new Segment.
After renaming the Segment, click 'Create Segment' and you'll be taken to the Segment view.
Click on the conditions and you will be able to edit them if you wish to.
Your new copied Segment will update automatically.