Updating 60.000 accounts/contacts.?

Updating 60.000 accounts/contacts.?

I have Zoho Enterprise with about 60.000 accounts/contacts, imported some months ago.

My mother-database is in ACT18 and I can make a CSV files of all those addresses/fields,of which many are
updated with new and updated data.

I like to update (and if not in Zoho, add)    the ZOHO database with the outside CSV file, how to do that, by batch,what maximum per batch.?

Thanks.