Change from Possessory to Absolute Title

Hi. My parents house was not registered with the Land Registry, after their death the deeds could not be located, we applied successfully for Possessory Title. This happened 2 years ago, today we believe we have located the deeds within the achives of the SRA, they will be sent to me upon receipt of relevant documentation. 
My question is, how do we apply for the Title to be converted from Possessory to Absolute? Also, roughly how long could we expect this to take? We are hoping to sell the property in the forthcoming months and would want this to be finalised before the sale. Thank you in advance.

Hi Barbara - you can apply to upgrade the title as per section 3.2.2 of our PG - Upgrading the class of title (PG42) - GOV.UK
It will wait a while before being processed so once you have a confirmed buyer you can request expedition to start the processing sooner - Request an expedite - GOV.UK

Thank you for your prompt response and advice