There is no limit on the amount that you are permitted to convert to Roth. Whatever amount you convert in a particular year is reported on a Form 1099-R for that year that you receive from the traditional IRA custodian and that Form 1099-R must be reported on the tax return for the year in which the distribution from the traditional IRA occurred.
It's up to you to decide how much to convert based on how much additional tax liability you are willing to incur for that year.
