There are two options for you. The first is to upgrade the module by command, the second is by interface.
The thing is that whenever you change XML/Python files you will need to update your module as Odoo does not automaticly update the code at this point. (this is an idea that will probably come in Odoo 9 though)

Option 1 - by interface:
1. Go to settings and update your module list by clicking on 'Update module list'.

2. Search the module you've updated in your list, open it and click on update.
3. You should now see your customizations. However this does seem to fail once in a while for me, this is why I like option two.

Option 2 - by command:
1. Open up a terminal and type in the command ./openerp-server -u yourModuleName.
For example if you want to update the module sale it would look like this:

2. Open your browser, surf to your Odoo instance and open the module you've upgraded.
You ''ll see it is upgraded. 

if you change  the view or modify the Table or database you should restart the server and click update and upgrade ...

but for dynamic changes like button method call... on change event a single refresh is enough...

Here is a recipe i use while coding new modules:

python / xml_
1. modify views (xml file) - upgrade module is needed fro view to load in database
2. modify .py file : only methods are modified -  restart server / service is needed (recompile .py file)
3. modify .py file : add/change _columns dictionary ( v7 api!) - restart service (for new dict to load) and upgrade module (for loaded dict to apply/cretae new columns in db)
 

also:
Modifying css is visible on page reload so no restart or upgrade needed,
Modify js - upgrade module needed for new js to load properly

Hope it helps