I I think someone has hacked into my iPhone it’s been acting weird and things change by them self. Can I change my phone up address or what ever it is called. I do not want anyone to access me from the outside, how do I know I am safe?

Check your device list to see if there is a device signed in that you don't recognize. You can remove the device using the steps in the article below. As a precaution, change your password.

Apple ID device list -Check to see where you‘re signed in.    

 Apple ID Password Change.      

 What to do after you change your Apple ID or password - Apple Support     I suggest doing this before you change your Apple ID or password.

1. Your iPhone is extremely secure against hackers and malware/viruses. It almost definitely has not been hacked. 
2. Changing your IP address is probably unnecessary at the moment.
3. It would be helpful if you explained exactly what is wrong with your iPhone. What do you mean "things change by them self?"