There are a few things that could probably all be done at the same time...Yellowing can have many causes and with the info/pic provided, it's hard to say exactly what the root cause (there's another plant pun) likely is so at this point, you might take a multi-pronged approach.
- bigger pot to make sure the roots have room to grow
- tough to tell, but your soil looks very wet. if it's too wet, the roots suffocate and can't do their job of bringing nutrients to the plant. Try mixing in some perlite when you transplant to help with drainage. Just as importantly, pay close attention to how much and how often you water and adjust based on your plant's behavior.
- when you up-pot, add a little nitrogen to your soil. your method will be different if you're growing organic or with synthetic nutrients
- get the environment dialed in...temp, humidity, ventilation, circulation, watering regime, lighting
The great news is it looks like you're paying close attention to your plants and you can tell that they're trying to tell you something. So, it's great that you're trying to figure out what they're saying! The other good news is it looks like they're overall healthy and with some small adjustments, you'll be back on track for some healthy happy plants and a great harvest!