Lead Details - How to change No of Employees

Lead Details - How to change No of Employees

I need to make the "No of Employees" field in the Lead Details to where it will accept a range of numbers such as:  5-9 or 500-999 or 1,000+

The way it is now it will only accept numbers and no characters.  Is there a way to edit this field?  If not, is there a way to mass transfer that data to a new custom field?

Thanks!
Kathleen