how can I retrieve deleted text mmessages

You will not be able to retrieve any deleted texts unless you restore your iPhone from a backup that you may have created. The other thing is that if you restore your iPhone from a backup then your texts will only be as current as the day and time the backup was created. 

If you choose to restore your iPhone from a back that you may have created then here is how to do it-->>Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Good Luck.

Axel F