Virtualbox is not updating to Version 4.1. Why?
Solution 1:
Oracle treat point releases (4.x) as new releases, not upgrades (4.x.y).
As such - for stability reasons, some people continue with, for example, 4.0.x until either support for 4.0 is withdrawn, or sufficient bugs are flattened in the new 4.1.x releases.
The usual policy is to deinstall your 4.0 release before downloading and installing the 4.1 release.
All your previous settings and virtual machines are safe since they are stored separately from the actual package.
Since it is a new release, you'll need to also upgrade the Virtual Guest Additions for each Virtual Machine that you have.
Solution 2:
From one of the pages fossfreedom linked to:
Q: What is the proper way to upgrade?
A: Since version 1.6.0, you no longer need to uninstall VB in Windows, but can install it on top of the current installation. This can be done by running the installer and follow the on screen instructions. For Linux Hosts, just run the install file (.dep, .rpm or what package manager you use) as root. The package will be updated automatically. For other systems, it should be the same procedure. The one exception to this is due to naming clashes: you do need to properly remove an OSE package if you are replacing an OSE version with a PUEL versions (for example because you need USB support). All VMs are kept during the upgrade or when you uninstall VB.
Moving to a new major version can be problematic too for Linux users. If you want to upgrade, fully remove the old version and then install the new one. It is advised to purge residual config, but it is not mandatory. For Debian based systems, this can be done using the following command (or use Shift+Del in the package manager for complete removal):
sudo apt-get remove --purge virtualbox-2.0 sudo apt-get install virtualbox-2.1
Same goes for the upgrade to newer major releases, like 3.0.