I want to update my phone it’s old version 12 so other apps says you can’t download this your must be updated to version 13
I want to update my phone but there no update button or a new version for iphone6 mine version 12
An iPhone 6/6plus can't be updated beyond 12.5.6, 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.