The Messenger of Allah (sal Allahu alaihi wa sallam) said: “Good behaviour towards parents by which one can be courteous to them after their deaths is to pray the funeral prayer upon them, pray for their forgiveness, fulfill their religious bequests, maintain relationships with those relatives linked through them and honour their friends.” [Abu Daud]
Another Hadith informs us that: “Charity on their behalf after their death (also) earns reward for them.” [Muslim]
If a person were unfortunate enough not to have accorded due respect to his parents during their lives Allah (subhana wa ta’ala) in His infinite mercy allows this person too to make amends and save himself from Allah’s painful punishment in the Akhirah.
Your parents are the people who have been kindest to you after Allah (subhana wa ta’ala). Start fulfilling their rights now. You don’t want your heart to become so hardened with sin that you cross the point of no return and are denied doing good by them even after their demise.