You can use the APEX_CREDENTIAL package to change stored credentials either persistently or for the current APEX session only.

• CLEAR_TOKENS Procedure
  
• CREATE_CREDENTIAL Procedure Signature 1
  
• CREATE_CREDENTIAL Procedure Signature 2
  
• DROP_CREDENTIAL Procedure
  
• SET_ALLOWED_URLS Procedure
  
• SET_DATABASE_CREDENTIAL Procedure
  
• SET_PERSISTENT_CREDENTIALS Procedure Signature 1
  
• SET_PERSISTENT_CREDENTIALS Procedure Signature 2
  
• SET_PERSISTENT_CREDENTIALS Procedure Signature 3
  
• SET_PERSISTENT_TOKEN Procedure
  
• SET_SCOPE Procedure
  
• SET_SESSION_CREDENTIALS Procedure Signature 1
  
• SET_SESSION_CREDENTIALS Procedure Signature 2
  
• SET_SESSION_CREDENTIALS Procedure Signature 3
  
• SET_SESSION_TOKEN Procedure