I have installed my previous Magento 2.1.5 years ago by downloading , Now I want to upgrade to 2.3.2 using the composer. Can I directly do that. What issues may occur ?
First to need to change your php version to php 7.1 or php 7.2 because Magento 2.3.2 support php 7.1 or higher version.after this link to help you updrade Magento 2.3.2 via composer. How to update Magento2 using composer After successful install Magento 2 may issue available of admin page blank so go to this solution Magento 2.2.7 admin panel blank page
After run again all comand like updrade, deploy and flush. May helpful this solution . Happy coding.