The master timetable is available here:
https://adweb.cis.mcmaster.ca /mtt/
As Andrew said, the first thing you should do is make sure you're actually allowed to take the courses you want to switch into. If you go to the course calendar
http://registrar.mcmaster.ca /CALEN...ent/index.html and click on 'course listings', then the department you want, you can see the prerequisites for any courses you're interested in. If you're allowed to take the courses, check the master timetable to see if you can arrange it so that there are non-conflicting sections. If this is possible, go onto SOLAR and check if the business courses are available
before dropping your enviro sci courses. If they are, then try to get the non-conflicting sections. If you can't get into non-conflicting sections because they're full, you should be able to talk to the instructional assistant or prof for the course to get moved into a non-conflicting section. This is usually, but not ALWAYS possible, so make sure you email the person asap.