so i know there are videos and diets and shit like that. but i generally think that exercise does the best job. if you can give more time to exercise then that time can be for jiu jitsu which is one of the best all over body workouts there is. if you wanna burn fat, then push urself harder in training. roll at 70% instead 40% instead of doing the technique 10 times do it 50 times. when u roll instead of jsut lying there when your on bottum lift the guys up and throw them around. if you cant, then try until you can.
if thats not possible then when you wake up and when you go to sleep do some exercises. press ups, planking (core workout) sit ups, squats bicep curls. each week increase either quantity or quality. eventually you wil notice you can lift more weight more times.
look at where you are weak and focus on that. if you have a weak core. then focus more on core workouts. (make sure you get obliques aswell as abs. work on ur back aswell)
each night before i go to sleep i do fifty press ups, changing hand positions to work on different areas of my shoulders pecs and arms. and i do 10 slowly and then 10 explosively and back and forth. then i do 200 sit ups, making sure i get in rotations to work on my obliques and also go at different speeds to help get good mix of fast and slow twitch muscle fibres. then i do 20 bicep curls and a tricep workout on each arm and then i plank for 1 minute facing down, on my right side facing up and on my left side and then finally 50 squats. it takes about 10-15 minutes and when you do it every night, you will notice a big improvement. but start off small and work your way up to doing more and more. my goal is doubling what i can do now.
have fun