u can change institution anytime however u need to make sure ur not violating ur study permit requirements like u cannot stay in Canada if ur not enrolled in any college. meaning u cannot have a gap of 2-3 months between u leave one college and join another that may cause problems. also, u need to check if the new college is on DLI. Also, u need to notify CIC
read more on the following link
" If you applied for a study permit to attend a post-secondary institution after June 1, 2014, you must notify Citizenship and Immigration Canada (CIC) via your MyCIC account every time you change institutions. You are not required to apply for a new study permit when changing institutions that are at the same level of study (e.g., from a college to a university).
For example, you must notify CIC if you submit a letter of acceptance from the University of Ottawa when you apply for your study permit but then transfer to Carleton University once you arrive in Canada.
You are not required to notify CIC when you change institution if:
you applied for a study permit prior to June 1, 2014;
you were issued a study permit to attend an institution at the primary or secondary level; or
you obtained a study permit as the family member of a study or work permit holder (i.e., you were not required to submit a letter of acceptance when applying for a study permit).
Get step-by-step instructions on how to notify CIC that you have changed DLI’s using your MyCIC account."
http://www.cic.gc.ca/english/study/study-changes.asp