We will arrive at Capital Airport by 2:30pm, and we want to take the train to Shanghai that same day

First of all, the express train only goes to Sanyuanqiao Station and Dongzhimen Station. Thus upon landing, you can take it to Dongzhimen first. It takes around half an hour. The ticket fare is CNY 25 per person. Then take subway line 2 to Xuanwumen Station and line 4 to the South Railway Station. After arriving, there are many bullet trains that can take you to Shanghai Hongqiao Railway Station. The train takes around 6 hours. The ticket fare of second class seat is CNY553, first class seat is CNY933 and business class seat is CNY1748.
In addition, you are advised to book the train tickets in advance. TravelChinaGuide provides online ticket booking service.The contact number is bookingtravelchinaguide.com.