Autogrowth in SQL Server
But before changing that I want to know can we do this change in working hours or do we require down time for it


Yes you can change the autogrowth setting when database is being accessed, for next autogrowth instead of percentage the value in MB would be taken into account. Its almost always a good idea to keep autogrowth in MB. You can get tentative value for autogrowth from This Article use the query mentioned to set the tentative value. Keep monitoring using the query in future this value may change then accordingly you have to change yours

I suggest you to read Considerations for the "autogrow" and "autoshrink" settings in SQL Server