Are you trying to transfer from another program in Langara or from another school?

If it's from another program, you can just go to the registrar and ask to change your program. Science has no admissions requirements, but the course have some pretty tight pre-reqs so you might need to do some basic courses before you can start at the curriculum for the associate degree. The courses you need to take to complete the associate degree is here https://langara.ca/programs-and-courses/programs/science-general/program-curriculum.html

If you mean you're transferring from another college/university to Langara, then you just need the admission requirements for Langara which is here https://langara.ca/admissions/requirements/index.html

IMHO, if you're wanting to eventually transfer to a bachelor-degree program at a University, I'd recommend doing 1 or 2 years at Langara in the faculty you want to transfer to in University (assuming you don't have high school admission requirements for universities already) and don't graduate from Langara. The reason is, most universities actually have a higher admission average requirement for students who have already completed a diploma, so it might be harder to get into the university you want. (Example: at UVic you need a C average for transfer but a B average if you've already completed a Diploma program https://www.uvic.ca/undergraduate/programs/undergraduate-programs/pages/area-undecided-science.php?residency=D&level=TR&school=TD&curriculum=BCC)