How to correct picture distoration

[ModernClassic]

Hi,
I got this no so old " funai " colour TV ( 10-15 years ? )from a friend and found that I like the picture quality over the modern ones with digital circuits.
The problem is the picture is distorted - reverse of a barrow: widened at the 4 corners and narrow at centre.
I seemed to recollect that there are some adjusters at the picture tube neck for that.
Would someone direct me as how and which control to adjust?
Thanks