DEFINITION NO FURTHER A MYSTERY

As a learner, it can only at any time practical in your case to tell apart /ʊ/ and /u:/, not /ʊ/ and /u/, and you can try this by size.then thrust your tongue upwards towards the top of your respective mouth, behind your enamel (I believe's called the tough palate but I am unsure), leaving all the remainder of your mouth exactly while in the /i/