Changing the blade on a retractable knife is an easy and straightforward process. First, you'll need to make sure that your knife is already in its closed position. Once it's closed, twist off the end cap of the handle – this will release any tension or pressure that may have been built up over time. You can then slide out the old blade and replace it with a new one. It's important that you get blades specific to your type of knife as they come in different sizes and shapes which are designed for particular knives only. Make sure when reinserting the new blade that it fits snugly into place before putting back on the end cap and twisting securely so there won't be any slippage when using your knife later on. And there you go - you've now successfully changed the blade!