Can I convert from 401(k) to Roth IRA?

Yes, you can. But remember, once you move money from a pre-tax retirement account like traditional IRA or 401(k) to a Roth, you need to pay taxes on that income.

Yeah, you can (but it wasn't possible before Jan 2008) and practically you'll get few benefits for doing that.
Typically, Roth IRAs have more investing options than 401(k) retirement plans. With a Roth IRA, you have more control over your investment options than in a 401(k) retirement plan. And the most importantly, Roth IRAs provide investors with the ability to withdraw not only their contributions but also their earnings, interest and dividends tax free in retirement.

It makes sense to convert 401(k) to Roth IRA in the following situations:

You expect that your income will increase in the future.
You want to withdraw money only when you're ready

You can do it as there are certain flexibilities. But, it's better if you talk to a financial advisor and know the pros and cons before doing it.