According to the release notes GUI v0.14.1.0 includes blockchain pruning. How do I utilize this feature with the GUI (monero-wallet-gui)?
First, note that this requires approximately 30 GB of additional storage, as, initially, the Monero software will store both the 'old' non-pruned blockchain and the 'new' pruned blockchain. You can, after verifying that your GUI runs properly, delete the old file of course. The following steps are required to use blockchain pruning:
 Make sure all Monero related processes are closed.
 Browse to the directory v0.14.1.0
monero-wallet-gui is located.
 If you are using a custom data directory, skip step 4 and proceed to step 5.
 Run the
monero-blockchain-prune tool (on MacOS, you will have to right click ->
Show package contents ->
monero-wallet-gui.app in order to see the tool). Note that this may take quite some time to complete. Thus, I'd advise to run it overnight.
[5a] Windows - custom data directory:
Open a new command prompt / powershell from the directory of
monero-wallet-gui. This is done by first making sure your cursor isn't located on any of the files and subsequently doing SHIFT + right click. It will give you an option to "Open command window here". If you're using Windows 10, it'll, most likely, give you an option to open the Powershell.
monero-blockchain-prune.exe --data-dir path\to\preferred\data\directory (Win 7 + 8)
.\monero-blockchain-prune.exe --data-dir path\to\preferred\data\directory (Win 10)
[5b] Linux - custom data directory:
Open a new command terminal from the directory of
./monero-blockchain-prune --data-dir path/to/preferred/data/directory
[5c] MacOS - custom data directory:
Go to your desktop.
Open a new terminal (if don't know how to open a terminal, see here).
monero-blockchain-prunein the terminal. It should add the full path to the terminal. Do not hit enter.
Note that aforementioned text will be appended to the path of
monero-blockchain-prune. Thus, before you hit enter, your terminal should look like:
/full/path/to/monero-blockchain-prune --data-dir path/to/preferred/data/directory
Where the full path is, intuitively, the actual path on your MacOS.
 Note that
path/to/preferred/data/directory is a placeholder that should be replaced by the actual path. To reiterate, this may take quite some time to complete. Thus, I'd advise to run it overnight.
 After the
monero-blockchain-prune tool has finished, open
monero-wallet-gui and verify that it is running properly.
 You can now delete the 'old' non-pruned blockchain file.