How to increase storage in my iPhone?

How do I increase storage in my iPhone?

Delete everything you don't need

Unfortunately you can't increase the storage of your iPhone, that's because Apple doesn't allow you to install micro sd card or something like that, that will increase your iphone's storage

Iphone has a fixed memory and doesn't allow users to upgrading it due to they believe that if memories are movable they make the phone laggy so the only way is to do it in software way. You can delete unwanted data or if you have a jailbroken iphone, you can use icleaner which deletes some unwanted files like caches and frees between 1-5 GB.