How do I modify my current visitation if I’m the non-custodial parent?

I currently have my three sons during the school year every Thursday at 6 pm until I drop them at school in the morning and then pick them up again at my ex's at 6 pm on Friday and have them through Monday morning when I drop them off at school. Also in the decree, I have visitation every other Tuesday from 6 pm-8:30 pm. As I am starting to take career development classes, I can't pick them up on Tuesdays any longer and I would like to drop them off at my Ex's on Sunday at 8 pm. Can I do this without informing the court or changing my decree with respect to the visitation? I also have a feeling that my ex wife will give me a hard time with respect to this change and may want more child support any suggestions with this problem? I’m in Texas.