For updating the LearnDash plugin, you can take either of the three ways:
1) From the update API
2) Manual upload
3) Via FTP
You will receive a notice in your WordPress Dashboard, when an update is available. Click the update link to install the update.
You can review the updates in the LearnDash changelog.
Don’t See The Update?
You can navigate to plugin menu which often triggers the update notice, but if you don’t see the update as available, go to Dashboard >> update and click Check Again.
For updating manually follow below steps:
Step 1: Download the latest version from your account section.
Step 2: Deactivate and delete the version you have installed (no data will be lost).
Step 3: Once downloaded, go to your Plugin >> Add New and click Upload Plugin.
Step 4: Select the updated LearnDash file that you have downloaded and Click Install Now.
Step 5: When it’s finished uploading, click Activate.
How to do so via FTP, you can check the following link.
https://codex.wordpress.org/Managing_Plugins#Manual_Plugin_Installation
Remember: Always back-up your site before updating. We recommend using UpDraft Plus.