You should register the death within 5 days. (Please note though, that where a coroner is investigating the death this is not always possible and the registrars service accepts this may cause a delay.)
Most people tend to register the death in area where the person died. This means that you’ll be given the documents on you’ll need on the day.
You can register a death in another area but the paperwork won’t be ready on the same day and will take longer. If you chose this option the documents will be sent to the office in the area where the person died before then being issued to use. This usually adds on a few days and is what causes the delay.