I would wait until results day before you decide. I decided to drop one subject, after a poor grade, so I could focus more on the other 3 but it depends on how you feel and what your plans are.
I really wouldn't recommend it if you don't need to... Unless you enjoy your subjects and really don't want to drop one, go for it!
I did 5 a-levels and got AAADD lol but only because my school wouldn't let me drop one. Also, one of them is a 'native' language. For me organisation let me down with the 2 subjects, but I'm sure you can achieve the best grades with good organisational skills.