How do you delete old apps that you no longer use?

See the following Apple articles:

Remove apps from iPhone

Remove apps from iPhone – Apple Support (UK)

Delete apps on your iPhone, iPad, and iPod touch

Delete apps on your iPhone, iPad, and iPod touch - Apple Support

If you delete an app, it doesn’t cancel in-app subscriptions that you might have. While deleting an app, you might see a Cancel Subscriptions option. Learn how to cancel your subscriptions.

If you cancel a subscription, It is not possible to delete the subscription that you have canceled.

This will disappear from your purchases after about a year.

Hide purchases from the App Store

Hide purchases from the App Store – Apple Support (UK)

This is quite a simple action - if you are on IOS you need to long press the app you wish to remove, then select delete it will prompt you to either remove it from the home screen (this will still keep the app) or select remove and delete all data. The second option will delete the app for you - this also works on Mac OS too.

Hope this helps :)