Point to note: If you did any changes on any plugin files, then keep backup of them, so that you can upload those files again after updating the plugin.
You can update plugins by following below steps–
1) Login to your wp-admin
2) Go to Plugins > Installed Plugins
3) Now, delete those plugins which you want to update.
4) Now, go to ‘Appearance > Radiantthemes Install Plugins’ (For some themes it's 'Appearance > Install Plugins'). If you're getting 'Update' option, then click on 'Update' to update those plugins.
If you're not getting the 'Update' option (This option is not available for all themes), then re-install and re-activate those plugins again and you'll get the updated plugins.