In PostgreSQL, the `UPPER` and `LOWER` functions are used to manipulate the case of text strings. Here's a quick explanation of each function with an example:

UPPER Function:
The UPPER function converts all characters in a text string to uppercase.

Syntax:

UPPER(string) 

 
LOWER Function:
The LOWER function converts all characters in a text string to lowercase.

Syntax:

LOWER(string)