• Right click on the Bitcoin file, then select the "Copy" option.
• Right click on the desktop and select "Paste".
• Right click this shortcut, select "Properties" and replace the command field with bitcoin-qt -datadir=path, where path is the fully qualified path to the new data directory.
• Double clicking the resulting shortcut starts Bitcoin Core with the custom data directory.
Another way:
• Open file browser.
• Select View -> Show Hidden Files menu option.
• Close Bitcoin Core if it is running.
• Copy the default .bitcoin folder to new directory(here, external drive).
• Rename default folder .bitcoin to something else. Eg:- bitcoin-old.
• Open Bitcoin Core.
• A window[1] appears asking you to choose a location. Choose Use a custom data directory option.
• Type the path to new directory in the field or click the ... button to point to the new location and click OK.
[1]
Source: http://bitzuma.com/posts/moving-the-bitcoin-core-data-directory/.
