i will give you my advice ; your work permit will be expired within few months and you will not be able to renew it so you will have to change your status in canada from a worker to another category. you want to change it to a visitor, in my opinion, don't do that ,change it to a student rather than visitor to be able to extend as long as you are a student in canada.
you asked about the way, it is very simple, you can't change your status from worker to student from within canada it means that you can't transfer from a a worker to a student or a visitor by sending an application to the immigration department.
you will have to fill in the application form for the visitor or student
(outside canada).
and not the application for extending your stay here in canada. after that you will have to prepare all of the required documents such as the financial support, the acceptance letter from the educational institution (let us say for example to study english language) and try to get the acceptance letter for a long period of time in order to get study permit for a long time, after you fill the application form for the study permit send it with all of the required documents ( passport photocopy, your current work permit photocopy, financial support,acceptance letter,that is it. and send all of them to visa office in buffalo,NY. they will process your application within 2 months or less if everything is ok in your documents they will ask you to send your passport to them in buffalo to stamp the visa and send it back to you and when you receive the passport with the student visa you will have at least go to the us border to get your study permit on the port of entry my friend had done the same and changed from a visitor to a student from within canada and he got a study permit for 4 years and his visiting visa was only 6 months,the whole process doesn't take more than two months if you have all of your documents ready.
use the application forms on this link :
http://www.cic.gc.ca/english/information/applications/student.asp