Your bank will gladly help you convert your Indian savings accounts into NRO savings accounts. You cannot change these accounts into NRE accounts directly; NRE accounts are supposed to be funded via deposits made from foreign currency accounts. Under the liberalized schemes available now, you can transfer the money in your regular savings account into your account abroad, converting it into foreign currency, if you (and your CA) provide proof to your bank (and the Reserve Bank of India) that you have paid all applicable taxes on the money in your savings account. And then you can transfer it all back into your NRE account. Perhaps you can combine these two steps into a single one, thereby putting the money in your regular savings account into an NRE account in one step, but I am sure that there will be lots of fees involved (e.g. you might get whacked by commissions, as well as the exchange rate differential as if you converted Indian rupees to US dollars, say, and then converted the dollars back to rupees) just as if you did the two-step conversion.
There are no taxes involved in moving your own money into different accounts but there can be lots of fees and service charges.