First uninstall old product before updating?

Have to? No.
Generally advisable? Opinions vary, but the broad consensus seems to be yes. TIH 2012 makes some very significant changes to DiskDrive and Volume device class handling and the filter services-drivers involved.

In either case, the very first thing you want to do is to create at least one full system backup. In fact, I'd recommend two: one with your current TIH version, and another with your native Windows backup feature.

It's also possible to export your current TIH settings. But whether the new TIH version will actually import and use them successfully appears doubtful at best.

Ok thanks. So I will first deinstall the old version.

PLEASE make yourself at least one full backup first. If you read some other user experiences posted here, you'll understand why.

Ok, but if my system could crash if I deinstall the old version, would it not be better not to deinstall it first?

And it's an update from 2010 to 2011 and to 2012.

No, Kurt. Not before you insure that you have a full system backup available in case it's needed to recover from a crash at any point. If your current TIH installation is working okay, using it to create a backup shouldn't be a problem. If it isn't use Windows own backup. Or, for greatest safety, use both.

In addition, make sure that you have bootable "rescue" discs available for both TIH and for your Windows OS. In the latter case, the Window installation disc can serve that purpose if you have one.

THEN, you can uninstall your old TIH version and install the new one and you'll thus be protected if either part of that uninstall-install process results in a failure to boot normally as can sometimes happen for various resaons.

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That last sentence of yours got edited in after I posted the above. I don't understand why you're going from 2010 to 2012 via 2011 instead of directly.

Thanks. It's an update from 2010 to 2011 and to 2012.

If I'm deinstalling version 2010, do I have to delete something in the registry or delete some folders manually? I mean for having it really clean deinstalled.

I'll make you a deal. I'll answer your registry question when you tell me that you've made a full system backup. Okay?

I have made a full backup. ;)

Okay. Good.

First of all, if all goes well, your version update will make all of the necessary changes in your system registry. In that case, count your blessings and be happy. There's nothing that you need to do yourself with any part of registry's CurrentControlSet branch.

It's only in cases where the update process or processes go wrong (the more of them, the greater the risk) that you could end up with versioning conflicts, either in your registry, or in your \Windows\System32\Drivers folder, or both. If that happens, you'll soon know about it one way or another. In the worst case scenario, your system startup will fail completely and you'll be very glad that you have a full backup that can take you back to the previous stable condition. To restore it, you'll need to boot to the appropriate "rescue" environment and so you'll be glad to have those too.

Good luck.

Thanks. I just updated and it worked everything well.

Great. But you're not quite "out of the woods" yet. If you use removable storage devices (especially USB-connected devices) check to ensure that all of them are still being recognized and are fully useable, both by Windows and by TIH 2012. If not, you may still want to revert.