In this guide, the procedure for re-syncing Geth on Windows will be shown. I am using Geth 1.5.4 (latest stable version as of 30 Nov) on my Windows 10 machine.
Note: If you have not installed Geth, please install Geth using the instructions here: How To Install Geth In Windows.
Resync of the blockchain has the benefit of reducing the amount of disk space used by Geth. The deletion of chaindata folder and resyncing of the blockchain will not be needed once Geth has employed state-tree pruning which will automatically archive old blocks to reduce disk usage. Until Geth has included this functionality, the regular deletion of chaindata folder and resyncing of blockchain is recommended to keep the disk usage at minimum.
Instructions For Windows
Step 1: Locate the chaindata folder
The chaindata folder is located at C:\Users\<your user>\AppData\Roaming\Ethereum\geth\.
Step 2: Delete the chaindata folder
Yes, delete the whole folder. Do not worry. Your Ethereum account will NOT be deleted (they are stored in another location).
Step 3: Run Geth with the -fast -cache=1024 flags
If you do not know how to set the flags, please use the instructions here (Under Step 4): How To Install Geth In Windows.
Step 4: Wait for Geth to complete the fast sync
Fast sync is completed when Geth starts to import 1 block at a time.