How to hold a high note note longer ?

In singing I can sing the high G in about 33secs i do it steadily I already breath from the diaphragm I want to hold it longer the longest I've held it was 44 seconds but it was crackling and not steady (it messed up at 34 sec so I came to the conclusion that 33 sec was as long as I could hold it ) I want to hold it longer any advice OH AND WHAT ARE SOME THINGS YOU GUYS DO TO IMPROVE YOUR RANGE AND HOW DO YOU SING AS IN WHAT ARE YOUR TECHNIQUES :D thanks