It may happen that travel plans change and you will face changing air or train ticket. Each ticket is a separate list of rules and conditions.
Returning air ticket bought online
The e-ticket purchased online can be returned only if this is a refundable air ticket. If in the notes of the ticket there is a statement that ticket is non refundable there is no chance you can return it and get reimbursed. Refundable tickets are those for which a traveler will get back a certain amount.
Refund for the e-ticket will depend on tariff you have bought it. Read carefully notes that are pointing out which percentage and under which conditions will be reimbursed to the traveler.
Cancellation of e-ticket online
If you have registered on air tickets sale website you need to access your account, using email and password that was created during the registration. The e-ticket you bought will be in the database. All access details should be available in the email, automatically sent to you when the e-ticket purchase was completed.
If you are not sure about the conditions of the ticket bought, you can always check with the airlines.
Find support section and send your request/question to the support team.
Usually they reply within 24 hours. They will also advise you on the amount you are eligible for refund, explaining which charges have been withdrawn.
If you feel comfortable returning the ticket online and performing all needed actions on your own, make sure to read carefully all the details and conditions of e-ticket cancellation.
When you confirm that you accepted conditions of ticket cancellation or return, your current ticket will be terminated and a new one issued if requested so. If no new ticket is bought the funds will be reimbursed to your credit card or other acceptable way specified by you and accepted by the air ticket company.