There are two ways to do it :

First Way {recommended}:

1. Download the latest WPLMS Package from Themeforest.
2. Unzip the package, unzip wplms.zip
3. Get the latest layerslider plugin from wplms->plugins.
4. Upload this file in your server via FTP at location wp-content/plugins
5. Delete the current Layerslider folder and unzip the uploaded package.

Now you have the updated Layerslider.

Second Way :
1. Deactivate WPLMS Theme
2. Delete the Layerslider plugin form Plugins.
3. Download the latest version WPLMS 
4. Unzip the package and unzip wplms.zip and Get the Layerslider plugin from WPLMS -> Plugins folder
5. Upload this plugin to your WP setup.
6. Activate the WPLMS theme.