Hi Daniel:

Both of them do the same thing. Make sure you follow the following steps while updating through the app:

1. Restart Odoo after you have copied your changes into the addons or extra addons directory.

2. Log into Odoo as an administrator user.

3. Go to Settings > General Settings, and Activate the developer mode 

4. Go to Apps and click on Update Apps List 

5. Search for your custom module and install/upgrade it.

You can update module either user interface or using command in terminal.

Restart server is required in both cases, If python file any code added.

After restarting server, you can update module in user interface.

Or

Using command terminal update module, server stop and update module below command

./odoo-bin -u module_name -d database_name

can I upgrade a module without this command ?

Yes you can update the module without command. using user interface but restart odoo server is required.