Hi Mona,
did you just do a clean install or an upgrade from a previous version of UM?. Or are you talking about updating in general?. 
Did you choose auto install which would create your partitions for you or did you create your own partitions?.
You could try the "Something else method" to recover your install if you have a root and home partition!.
There may be a problem with your install media (USB stick not fully functional?). Also:
Let us know more details about your install process please!. 