Hi Lang3,
QuickBooks Desktop is a versatile program that simplifies the way you manage your work. Rest assured, I'll be happy to share more info so you're on the right path.
In order to reduce the number of customers in your file, you're more than welcome to create a new company file from an existing one or export the information using IIF. You can pick the data you'd like to migrate to the new company file. Feel free to check out the following article as it sheds more light on this: Export files in QB Desktop.
You also have the option to create a company based on an existing file. Doing this brings balances and lists such as customers and vendors from your old company file. To do this, go to File> Create Company from Existing Company File > Select the current file and create a name for the one you're creating.
Give this a try and let me know how you make out. Otherwise, if you're looking to upgrade, feel free to check out this article here with more info.
