I would give Sansa Tech support a call. They have a way to do this and will walk you through it. Write down the steps you take so if you have to ever do it again you will know how.

Americas Technical Support

North America Technical Support
1-866-SANDISK (726-3475)
7 days a week:
4am. - 10pm. Pacific Standard Time
7am - 1am Eastern Standard Time
support@sandisk.com

Holiday Hours
Dec 24 - 7am - 7pm Eastern Standard Time
Dec 25 - CLOSED
Dec 31 - 7am - 8pm Eastern Standard Time
Jan 1 - normal business hours

Tired of waiting for your device to do what you need it to?