Removing name of joint owner fron registered agreement for sale

execute registered relinquishment deed 

The title (sale) deed of the property has your name also?

Thereafter as per your post you have signed agreement to sell.

You may consider suitable deed e.g; relinquishment/release, sale deed to dispose your share in favor of your friend.

Cover the amount paid by you to friend.

The agreement ot sell may be amended as per the deed disposing your share by taking buyer in confidence..

Preferably approach in person  a very able senior LOCAL counsel of unshakable repute and integrity specializing in Civil matters and well versed with latest citations, LOCAL applicable rules/laws/ … and having successful track record…. and worth his/her salt…..and share inputs /show the documents/evidence for a considered opinion..and to draft the deed covering your long term interest.

At each location three are some counsels that specialize in such matters and they are well known.

Check for such counsels at LOCAL civil courts, HC, SC……