Seems like it's permissions issue.
1: Press win+r shortcut on the keyboard >> enter %programdata% in the window that will pop up and press enter.
2: Navigate to the Apple\Apple Application Support folder
3: Right click on the kdrl directory and select properties, then select security tab.
4: In the 'Group or user names' box, there should be the following entries;
- Administrators (name of your computer\Administrators)
- Users (name of your computer\Users)
If necessary you can add them using the Edit button and then Add.
5: Set the permissions for these user names as stated below:
- SYSTEM - check all boxes except 'Special Permissions'
- Administrators (name of your computer\Administrators) - check all boxes except 'Special Permissions'
- Users (name of your computer\Users) - check Read & execute, List folder contents and Read.
6: Rember to click 'Apply' after setting up each user name, and when you are done, just OK your way back out of the properties dialog box.
Try to update iTunes now.