Note : Magento 2 version should be greater than 2.1.19
To resize the image follow the steps below:
- In Magento Admin Panel, Go to Stores → Configuration → Klevu Configuration → Product Image Settings
- Modify image width and height
- Click on the Save Config button
- Once you have changed the settings, please perform full sync by following the steps specified at the following link : Performing Full sync for the Store