To manage your advanced segments, navigate to the gear icon pull down menu at the top of your reports and select Avanced segments. The management screen will appear, as shown in the following screenshot.
In the Action column you have the following options:
Copy: If you want to build another segment based on an existing segment without affecting the original segment, then click copy next to the segment you want to build off of.
Delete: Allows you to delete the existing advance segment.