1- you need a remote access to the server

2- you need to download the code of the module(s) you need to install

3- you need to configure your odoo instance to use the new addons in the addons_path option in the config file used to run the instance like:

[options]
; This is the password that allows database operations:
; admin_passwd = admin
db_host = localhost
db_port = 5432
db_user = odoo
db_password = odoo
xmlrpc_port = 8069
addons_path = /home/aek/odoo/odoo-8.0/openerp/addons,/home/aek/git-workspace/solt-med-odoo-src/addons,/home/aek/git-workspace/solt-tools-odoo-src/addons

4- you need to set correct permission on the files and folders for the Odoo instance running user, like:

chown odoo -R /path/to/your/addons
chmod 755 -R /path/to/your/addons

5- you need to restart your Odoo instance

6- you need to update the module list in your database by setting the technical feacture group in the admin user, refresh the browser and then just clic on the menu Settings/Modules/Update Module List and clic on the Update red button that shows up in the wizzard

7- Find your module(s) to install it