my iphone 6 fast heat and can’t suipport several apps

An iPhone 6 can't be updated beyond 12.5.7, it doesn't have the hardware needed to run anything higher.

If you need a higher iOS version, you will have to purchase a newer phone.

To update to 12.5.7 -

Go to Settings > General > Software Update.

This link will show you how to update your iPhone, iPad, or iPod touch using WiFi -

Update your iPhone or iPad - Apple Support Update your iPhone or iPad - Apple Support

This link will show you how to update using your computer -

Update iOS on iPhone - Apple Support Update iOS on iPhone - Apple Support

zadsvill ~ Does your iPhone 6 still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health

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