I have an 18 year old argentin sensation but his stamina is only 5 how do i improve it?

hmm, not sure whether this should be in this forum, but who cares.

If it where CM01/02 id say stick him on Physical.

But as its CM4, i would say get him to do a lot of physical training, weight lifting, cross-country etc. ALSO, the more you play a player, the more match fit he will become, so give him a few tries from the bench.

TROD.