It can be retrieved in two ways:
Via GUI:
1. Connect to server
2. Connect to the database
3. Click on the database and expand--> Click on Programmability --> Click on stored Procedure --> you will get the list of procedures
4. Right click on procedure name à script stored procedure asà create to à click on New Query Editor window, the you will get the procedure in a new window, you can edit it and execute it again to save the changes on server.
Via Command:
1. Connect to server
2. Connect to the database
Query: sp_helptext 'Procedure_name'
Execute the query( using F5/ execute button)