How can I import data into blank field an existing Account record?

How can I import data into blank field an existing Account record?

Is it possible, to import via a CSV file, a value for a field which exists upon the Account record.  For example, for the account for company name ABC123, I wish to import the QTD Revenue Achieved.  Obviously, this value will change and with some moderate frequency, I'd like to do a mass import into this field for all of my active Accounts as I have new and updated data.   Is something such as this possible or is the import function just to create new Leads/Accounts and not the ability to update individual field names within a record?  Thank you.

KReynolds
Kount Inc.