How do I inform Companies House the company's registered office address has changed?

The easiest and quickest way to notify Companies House of this change is online via WebFiling.

However, if you do not have the facility to file online you can download a Change of registered address form AD01, and on completion send to
Companies House
Crown Way
Cardiff
CF14 3UZ.

How to change your accounting date for Limited Company

A company or limited liability partnership (LLP) can register to change its accounting reference date (ARD), provided the relevant accounts are not already overdue. Private companies have nine months after the ARD in which to send their accounts to Companies House, or 21 months from date of incorporation if the first accounts cover more than 12 months.

You can shorten an accounting reference period as often as you like and by as many months as you like.

When a company shortens its accounting period, the new filing deadline will be the longer of:
-nine months for a private company (or six months for a public company) from the new ARD
-three months from the date of receipt of the notice.
For additional information on changing your ARD, see the guidance notes on ARDs on the Companies House website.

How to make the change
Complete form AA01 online via WebFiling and submit to Companies House .

Alternatively, you can complete a paper form AA01 or LL AA01 for LLPs and then return it to Companies House by post. Remember that you cannot request a change if your accounts are already overdue.

Source: http://www.businesslink.gov.uk/bdotg/action/detail?itemId=1073792136&type=RESOURCES