SQL Update of MD5 Passwords

Question

I am new to PHP & SQL. I am trying to update a password from my database and I cant figure out the SQL statement so I done some research and came across this SQL statement:

UPDATE `Users` SET password= passwordmd5 (password)

I then added a bit more to the code as follows:

UPDATE `Users` SET password= tony123 MD5 (password) WHERE user_id = 55

I get the following error:

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'MD5 (password) WHERE user_id = 55' at line 1

What do I do?