I applied to SLO with General engineering, but I think I am going to change it to Mechanical, or bioengineering. I wanted to know if it is going to be difficult to switch majors at SLO?
Not at all if you are transferring to the same college. Switching from general to mechanical or bio medical should be relatively easy! I know quite a few people who have.
General engineering is a big feeder into other, more specific, engineering areas.
Below is a link that will outline some of what you need to know. Note, there are minimal GPA requirements to even be eligible and ME, at 2.75, is higher than the rest of engineering. Good luck.
http://www.academicprograms.calpoly.edu/content/academicpolicies/policies-undergrad/change-major
http://eadvise.calpoly.edu/switching-majors-with-ceng/
This link is specific to the College of Engineering. YOU wouldn’t have to have the normally required 2.75 gpa in order to be eligible to change into ME because you would be coming from GenE. To change to either BMED or ME, you will just need to be in good academic standing after 1 quarter (gpa >= 2.0) and meet the terms of your ICMA. My son’s ICMA for change of major into AERO required a 2.5 gpa in the ICMA required courses, CP gpa, and higher ed gpa. He just was officially admitted to AERO after winter quarter of his 2nd year. Good Luck! 
Thank you very much for the help. I appreciate it greatly.