I want to fly to Lanzhou from Shanghai in the middle of August. What is the temperature there

Generally speaking, the average temperature at that time is about 30 and rains little at that time. It will be cool in the mornings and evenings.
For the transportation, you can choose the public transportation, since the public transport system in Lanzhou is well developed, with 110 bus routes covering every corner of the city. Or you can choose to take the taxi, because the fee is not very high.
As for the hotel, Grand Solxe Hotel, Xilan International Hotel, JJ Sun Hotel are three good hotels in Lanzhou and you can choose one of them.
As for the places to visit, Waterwheel Garden, Ancient Silk Road, Five Springs Mountain Park and many other spots are worth to see. Here https://www.travelchinaguide.com/attraction/gansu/lanzhou/, you can find whatever you want to see in Lanzhou.
As for the restaurants, you can enjoy the local food in the hotel you live in, since they have professional cookers there.