A. Yes you can.
You will have to pay tax on the money converted, but when you withdraw money from Roth 401K, you don't have to pay any tax anymore, just like you wold with a Roth IRA.
Although rollovers are permitted, not all employers offer this option.
A caveat: make sure you have enough money outside of 401K to pay the tax bill, otherwise you will have to pay an early withdrawal penalty if you have to take money from the converted 401K to pay tax.