As this is a very early release of Windows, it is not suggested that you upgrade your normal computer to the Windows 10 TP. Instead you should use a spare computer or even better a virtual machine like VirtualBox. If you decide to go the VirtualBox route, download the ISO and create a Windows 8.1 guest in VirtualBox. Then go into the settings of the guest and mount the ISO as a DVD. When you are ready to install, double-click on the guest to start the installation from the mounted ISO. It will install perfectly, but unfortunately at this time the Guest Additions will not work. I expect a VirtualBox update will be released soon that will allow the guest additions to work.
Windows 10 Technical Preview installing under VirtualBox
Included in the technical preview is a feedback application that you can use to give Microsoft feedback on the various aspects of Windows 10. Microsoft has stated that they want to hear from Windows users as the development continues, so if you wish to provide suggestions or bug reports to Microsoft this is the way to do it.
Windows Feedback Application
If you have any questions on installing or using the Windows 10 Technical Preview, please feel free to ask in our Windows 10 Forum.