Online math classes over the summer

I am a first year aerospace student, and I was looking at taking Basic Differential equations over the summer. Basically, first semester sank my GPA. So far semester two is going better, but the whole online thing might very well screw me over. I was hoping to try to take a class or two over the summer online in an effort to try and nudge my gpa up to at least a 3.0. I'm just looking for input on summer classes they have taken online as to whether they are easier or harder. for perspective, I ended up with a C in calc II, and I'm looking at getting either a high B or low A in calc III. Also, teacher recommendations for differential equations would be appreciated as well.