Do I have to delete the Apple ID?

You don't have to delete the ID. What happens when you try to reset the password? Where are you having problems logging in? Is this a new iPad?

If you have changed your ID or password, have you followed the steps in this article?

What to do after you change your Apple ID or password - Apple Support.      

More information would help.

You won't be able to delete and Apple ID unless the know the associated password. In trying to recover the password, have you been using:

See If you forgot your Apple ID password https://support.apple.com/en-us/HT201487 or

You also can use Having trouble signing in/iForgot https://iforgot.apple.com/password/verify/appleid 

If not, try using one or the other. Assuming you have been using one of them, have you been asked to answer the pertinent security questions? If yes, then what happened? Along the way you should have been asked to provide security question answers (or to have been sent a verification code related to two-factor authentication).

Do you have access to another WiFi network where you can try? That has worked for several people.

Try a restart.

Restart your iPhone, iPad, or iPod touch         

Try a forced restart.

Reset Device.      

If necessary

Hard reset.        

Do a backup and try a factory reset. Then restore from your backup.

Restore to Factory setting.      

Backup - Restore your device from an iCloud or iTunes backup.