I ran the commands that you had provided above. They seemed to have resolved the "note writeable" problem with the Moodle plugin upgrade.
Now, before I go about updating the theme plugin I am using (i.e Adaptable), I wanted to share the output of the update plugin procedure:
Installing available updates
Debugging output enabled
Downloading theme_adaptable ... OK
Validating theme_adaptable ... OK
[OK] Name of the plugin to be installed [adaptable]
Help with Name of the plugin to be installed
[OK] Plugin version 
[OK] Required Moodle version 
[OK] Full component name [theme_adaptable]
[OK] Declared maturity level [MATURITY_STABLE]
Help with Declared maturity level
[OK] Plugin release [1.6.1]
[Debug] Found language file [theme_adaptable]
[OK] Write access check [/opt/bitnami/apps/moodle/htdocs/theme]
[Warning] Target location already exists and will be removed [/opt/bitnami/apps/moodle/htdocs/theme/adaptable]
Help with Target location already exists and will be removed
[OK] Write access check [/opt/bitnami/apps/moodle/htdocs/theme/adaptable]
Validation successful, installation can continue
Should I proceed with the plugin upgrade? I have made an AWS AMI to be on the safety.
Please let me know if I should proceed and what the "Warning" message above means.