alex.witte thanks 

The database is big, maybe you could tell me where in database i change that?

thanks in advance

But the password have many numbers and letters encrypted with salt. 

What will happen if i remove that encrypted password and replace it with a "normal" password? Will that works? I not want to try it on my main admin account

did not works i test it on another user and if i input a not encrypted password in the database then it will impossible sign in with that user.

but change the username did working

Skadate, the password is crypted, you're correct the field won't accept just words. See screenshot. 

Find a user you joined website with. Copy his encrypted password and paste to the password of the admin. Then you'll be able to login with the password of that user.