You can’t. You get admitted to a school in Canada then you apply for a study permit. Your application is processed from your home country. Because you are in Canada it lessens your chances because you need to show strong ties to your home country.
There is no option to convert a visit visa to study visa. You have to apply for a study permit. Not everybody can apply for study permit inside Canada.
Only some people can apply for a study permit from inside Canada. Do any of the situations below describe you, or the person you’re applying for? (required)
You’re currently in Canada and one of these applies:
you have a valid study or work permit
your spouse, common-law partner or parent has a valid study or work permit
you’re a minor child in primary or secondary school
you’re an exchange student or visiting student
you completed a short-term course or study program required to be accepted at a DLI
you or your spouse, common-law partner or dependent child has a temporary resident permit (TRP) valid for 6 months or more
you’re being sponsored to immigrate and you already applied for permanent residence (if you’re eligible)
you or your spouse, common-law partner or dependent child are subject to an unenforceable removal order
you’re the spouse, common-law partner or dependent child of:
an athlete on a team based in Canada
a member of the media
a member of the clergy
military personnel on duty in Canada or
an accredited foreign representative
you’re a refugee claimant in Canada or a family member of a refugee claimant in Canada