What are the common methods for installing and upgrading the win10 preview?

Replace the current system (immediately upgrade the current system to Win10 technology preview)
1. After downloading the image, open the ISO image (Note: double-click on Win8/8.1, Win7 can be loaded with virtual drive), directly Run setup.exe from the mirror root directory as shown below.

2. Accept the license terms

3. Check the installation environment. This may take a while, depending on the amount of software in the system you are currently using.

4. After the check is complete, the installer will list things you need to be aware of, such as missing system features or existing software. Compatibility and so on. If there are no things to note, the results shown below will appear.

5. Here you can also change the content that needs to be retained after the upgrade. Click “change the content to be kept", the following image appears

6. Select the item to keep.
Note that no matter which option you choose, the current system will be replaced by the Win10 Technology Preview after the upgrade. The “personal files” refers to the contents of the “Users” folder; the specific applications can be retained depending on the compatibility of these applications in the Win10 preview; if you select “do not retain any content”, After the upgrade, “Personal Files” will still be saved and moved to a folder named Windows.old.

Click Next to start the installation. If you choose to keep all content upgrades, this can be a very time consuming process.
The disadvantage of this method is that it cannot perform a formatted installation (ie, a clean installation).