Developing a module is an iterative process, and you will want changes made on source files to be applied and visible in Odoo.
In most cases this is done by upgrading the module: look up the module in the Local Modules list and, since it is installed, you will see an Upgrade button available.
However, when the changes are only in Python code, the upgrade may not have an effect. Instead of a module upgrade, an application server restart is needed.
In some cases, if the module has changed both in data files and Python code, you might need both operations. This is a common source of confusion for newcomer Odoo developers.
But fortunately, there is a better way. The simplest and fastest way to make all our changes to a module effective ...