Hello,
In very simple terms, if you sign the Deed, you are renouncing your right to a renewal of the lease at the end of the term of the lease. I beleive the Deed is usually signed at the same time as a lease is created (although I suspect it can probably be signed at any time).
If you have not already signed a Deed of Renunciation in times past, I would suggest you ask them to send you a new lease and ensure you sign all documents at the same time (obviously ensuring you have all documents witnessed, then keep a copy of all items).
Just my personal opinion... I'm not an expert.