Windows 10 Technical Preview Build 10049 has released but you can get problem while updating your PC to this new version, even though having gone to Settings > Update & Recovery > Advanced options, and setting Choose how preview builds are installed to Fast.

In this article, we will guide you to update your Windows 10 to Build 10041 successfully.
There are 2 ways to fix this issue:
Option 1:  Edit your registry
If you’re not able to install the update, you can instead edit the registry yourself.  A word of warning:  these instructions ONLY apply to devices on Build 9926 that have set Choose how preview builds are installed to Fast:
– Open regedit.exe
– Navigate to HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsSelfHostApplicability
– Ensure the following values exist:
        {value name}, {value type}, {value data}
BranchName, REG_SZ, fbl_impressive
ThresholdOptedin, REG_DWORD, 1
ThresholdRiskLevel, REG_SZ, low
  + Delete all other values
  + Open Settings > Update & recovery > Windows Update
  + Tap or click Check for updates

Option 2:  Install the Windows Update that will reset your Flight Registry Settings
You can download the update directly from the Microsoft Update Catalog: