Steps to Upgrade your iDevice to iOS 4.3.2:
Step 1: Download your Firmware from the Links at the end of the post.
Step 2: Download and install iTunes 10.2.1 from Here.
Step 3: Connect your Device and Launch iTunes
Step 4: Right Click on the iPhone Icon on the left in iTunes and choose “Backup” (backup process will take place)
Step 5: After Backup your Data, Hold down Shift (Windows) / Alt (Mac) and click on Restore.
Step 6: Choose your iOS 4.3.2 firmware you already downloaded!
Now Let the iTunes do some processes then your Device will be updated as soon as iTunes finish its upgrade process.
Direct Download Links for iOS 4.3.2 / 4.2.7