substitute string with another string in a table.field

Hello

the field USERS.CELL_NUMBER  has the following definition.

Datatype VARXCHAR2 size : 255 CHAR.  with this query I get all the conntents with '⁺' (that indicate 00 international prefix)

select first_name, last_name, username, cell_number from ELD2016S.USERS where CELL_NUMBER LIKE '%+%';

I need to substitute (replace)  all the character '+' with string '00'.

could you please help by giving the sql command to perform this .

thanks regards

Giorgio