Yeah so if you want to change employers as a carpenter:
1) Go to any carpentry company and apply for a job.
2) If they accept you, take job offer letter from them.
3) With job offer letter&confirmation from AIT you can go to the border and get new WP.
4) If you don't want to go to the border then you can apply online/paper but it will take more time.
That's pretty much the way if you are working in one of the occupation (estimator, welder, heavy-duty equipment mechanic, ironworker, millwright and industrial mechanic, and carpenter).
It's the easiest way, you don't want to play with LMO - it's a very long process (3 months and up).