I need to upgrade my current version of DNN this week. I am currently using 2.1.1. I don't want to do everything twice, so, I have several questions.
To be honest, I don't know. But I see that the DNN download page very strongly states that the 5.0 release-candidates are "NOT RECOMMENDED FOR PRODUCTION USE".
It's been my experience that DotNetNuke has a tendancy to release breaking changes without documenting them (or documenting much of anything, for that matter). Without knowing exactly what you have installed in it, it's impossible to say exactly how screwed you are. But I can guarantee you the transition will likely not be easy, especially if you have a lot of modules installed.
Between 2.1.1 => 4.9, so much has changed that I can't imagine there is any automated way to upgrade. You're better off starting from scratch and seeing what still works. Most likely you will need to find newer versions of any modules you're using, or replacements for those that aren't being kept current.
I personally strongly disagree with ALassek, you can upgrade DotNetNuke, you just have to follow the steps listed and as long as you do that it isn't a big deal at all, but there are a few key things to keep in mind as you set down the road to do your migration.
DO NOT USE 5.0 in production at this time. 5.0 is only in RC2 stage at this time and using it in production is NOT recommended and an upgrade path from RC2 -> Final might not be possible!
If you plan on trying to upgrade from 2.1.1 go from it to the most current version of 2, then go to 3, then go to 3.3.7, then go to 4.4.1, then to 4.6.2, then to 4.9.0. Typically you are able to make it, but some sites are not.
Some modules though will need to be updated to work with DNN 4.x, depending on the numbers and vendors this can be an easy process or can involve needing to find other providers for the specific functionality at hand.
As for the potential to upgrade to 5.0 from 4.9, yes, that will be 100% supported once 5.0 is in a production ready state.
There was a huge amount of breaking changes between 2x and 3x which will cause pretty much any custom modules you have to have to be upgraded or replaced. Other than that Mitchel is the DNN man and I would defer to him.