Heat the ironed- on letters using a hairdryer. Set your dryer to its hottest setting and turn it on, and hold it close to the letters. After a few minutes, the adhesive on the characters becomes malleable, making them easier to remove. If you don't have a hairdryer, steam off the letters using an iron and a wet cloth
To remove iron-on patches, start by placing a clean cloth or piece of wax paper over the patch. Then, press down on the patch with a heated iron for 15 seconds, which will melt the glue. After 15 seconds, remove the iron and peel the patch off.
You may find this helpful https://www.google.com/amp/s/www.thriftyfun.com/Removing-Iron-On-Labels-and-Patches-amp.html
I usually sew them on, so can be removed later.