Full roller release has the thumb rotating clockwise (RH) at release.  Semi roller release has the thumb rotation counter clockwise at release.  --  JohnP

Does this make more sense to you  --  full roller release, fingers start on the side of the ball and rotate to underneath it on release, semi roller the opposite.  --  JohnP

A good semi roller release starts with the fingers underneath the ball and as the thumb clears its hole the wrist rotates counterclockwise so the fingers come through on the outside of the ball.  --  JohnP

Have you video taped your release?  If not, ask someone to tape you and do a closeup of your hand as you release the ball, watch it at full speed then in slow motion.  Compare that to the better bowlers using a semi roller release (maybe you can ask someone to let you tape their release) and I think you'll find that your thumb is rotating up instead of down.  Sorry I'm having troauble finding the right words, I think I could help you in person easier.  And, dumb me, I just noticed your name which means you're left handed, so in my previous posts that mentioned clockwise or counter clockwise reverse what I said.  --  JohnP

No probs John... I am working at staying under ball, already ball track is somewhere between the full and semi roller, so seeing some improvement.. I do have a vid but it is only of my old style coming around the ball release... I have checked out Youtube vids a bit.. I think I am getting there slowly, but thanks for your patience and time with me lol..

Cheers mate
LL