Replacing old pot for nowt, he's overjoyed (2,3,2,3,5)
I believe the answer is:
on top of the world
'overjoyed' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'replacing old pot for nowt he's' is the wordplay.
'replacing' is an anagram indicator (placing again).
'old'+'pot'+'for'+'nowt'+'he'='oldpotfornowthe'
'oldpotfornowthe' anagrammed gives 'ON TOP OF THE WORLD'.
Can you help me to learn more?
(Other definitions for on top of the world that I've seen before include "as a polar bear, but not as a penguin?" , "as a successful North Pole expedition?" , "In seventh heaven" , "Delighted" , "as Hillary once was?" .)