Actually..

Here's a link.
Looks like the only thing you can convert to a ROTH IRA is a traditional IRA.

There is something called a Roth 401k. You would have to ask your company's benefits person if they are willing to change from the traditional 401k that they presently have to a Roth 401k. Each paticipant in the plan would have to recharacterize their present 401k accounts into a Roth 401k account. Which would mean paying all the taxes now. This might make sense for some employees but not all. Are you prepared to come up with the money to pay your taxes now out of your own pocket? If you are not happy with the returns you are getting perhaps its the fund choices you are making or perhaps its the Fund company itself. You might want to speak with the powers that be to see if they need to look a new plan sponser.

You could roll your 401K into an Roth IRA in another investment company BUT you must pay taxes on all that money during that transaction. Remember you have deferred all of those taxes in your 401K up to this point. Once this money goes into your Roth you do not have to pay anymore taxes on your interest you acquire.

Does your company offer the ROTH option? If not, Unless you have your own business that has income then a ROTH 401k is not an option period...a 401k has to be offered by an employer. As for rolling out money while you're still employed? That's only an option for a very few plans and only for employer contributed money. Any money you put into the plan has to stay there until you turn age 59 1/2 or you separate from service (quit or get fired).

If you're not happy with the returns then go to your boss and tell him..perhaps there are better options for your 401(k). Though the market recently hasn't been very good so likely that's the culprit more than the investments. Without knowing what options you have (fund names and class) I couldn't even comment about the quality.