I created a group in Facebook.
Now I want to change it to a fan page and retain the group members as fans.
Is there a way to accomplish this?
Unfortunately, no. From the Facebook Help pages:
I have a Facebook Group. Can it be converted into a Page?
It is currently not possible to convert Facebook groups into Pages. We recommend that you create a Page and notify your group members about it.
Even though there is no limit to the number of people your group can have, you will not be able to send your group a message if it has more than 250 members. If your group has more than 250 members, notify them by posting in the group.