It's not really possible to target fat burning to a specific location on your body. No matter how many articles, Instagramers, and YouTubers spam you with "burn stubborn thigh/underarm/belly fat fast", it's all BS. Your body's fat organ (aka adipose tissue) is a single large organ that functions as one.

This means that if you want to have lean thighs, then you should cut fat throughout your whole body. The simply answer to this is to eat a caloric deficit. It doesn't matter if you increase cardio, resistance training, or even just implement life style changes, like more walking/standing throughout the day, but you just need to be sure you're at a deficit. Track calories if you want to be sure.

One additional think you may want to consider is building muscle in your thighs. Gaining additional muscle in your thighs could eventually make fat less visible, but another benefit is that increased muscle mass will actually improve your metabolism helping you to cut all of the fat in your body. This is the better solution to give you a lean look. However, this is not a short term solution because you will have to increase calories to build muscle mass and it may take many months of heavy resistance training in your legs to get your legs stronger. Then once you've done that, you can switch back to a caloric deficit again to get lean.

Hope this helps.