There are more details in the release notes.
To enable block pruning set
prune=<N>on the command line or inbitcoin.conf, where N is the number of MiB to allot for raw block & undo data.
A value of 0 disables pruning. The minimal value above 0 is 550.
Where 550 is the size in MB you want the node to occupy in your system.
The bitcoin.conf is in the Bitcoin data directory, you can create a text file by the name there, if there isn't a bitcoin.conf yet.