Terrible upload speed

My plan is for 100/10 (premium?). I regularly check speeds through the cox speed check and speedtest.net. I normally get around 100 down but I not sure if I've ever gotten over 3 up. Usually around 2 - 2.5 up. It's painfully slow when I need to transfer files to my work, etc. Cox upgraded my modem to a DocSis 3.0 within the last year. What can be done to get my upload speeds up to par?