Wear summer clothes at that time. You can take subway Line 2 from Chongwenmen to Xizhimen Station, then walk to the Beijing North Railway Station for trains. If you want to take bus, get off at the next stop of Xizhimen, Jishuitan. Walk about 10 minutes from Exit to find the Deshengmen Arrow Gate. The 919 bus to Badaling is hebind the gate. Train is not bad to avoid occasional traffic jam by bus.

Thank you for your helpful response.
So if we take by train,
1) what type of transport do we need to take from Badaling Train station, e.g by foot or taxi?
2) is the Ming Tomb reachable from Badaling Great Wall or Train station?
Please advise.
Thank you.

Badaling railway station is located at guangcheng (Barrier Fortress), I think you may just go there on foot. It is easier from Badaling to Ming Tombs than Badaling train station. You may take bus no. 919 to Changping Xiguang, transfer to bus no. 314/22 (changping) to Ming tombs.