It's a very good question. Read the following lines which can help you:
1. Open "Contacts" app on your HTC Desire phone.
2. Open options and select hare Contacts.
3. Select contacts from your contacts list.
4. Select SD Card.
5. Then it shows information that you your contacts are saved in SD card by the name of xxxxxx.vcf
6. Open SD Card from File Manager.
7. Find that .vcf file.
8. Send it to your Xiaomi Redmi 2 Phone using bluetooth or Shareit/Xender.
9. Find a file in the file manager of Xiaomi Redmi 2 phone and install it.
Now all of your contacts which you want to transfer have been transferred from your HTC Desire phone to Xiaomi Redmi 2 Phone.