You may have to research a little on this forum (you can probably read old postings of this thread). Based on my own experience relink does not work and an easy way to get around that problem is to file a second 485 (people might scare you). However, there are people (who have posted in this thread) that have managed to file the second 485 and got an approval in less than 4 months or so.
Check the posting of 00000 on August 7th in this same thread which shows 2nd 485 was successful and relink does not work. You will find some more if you go far back...
Relink is a hit and miss story. If you want a remedy that is sure to work, try second 485.
Consult your lawyer too. Usually, they don't want to invest time to file second 485 (no extra $$ there) and so might discourage. Be specific and ask him/her what is the draw back in filing second 485. Usually, USCIS sends out a RFE asking you which 485 you want to pursue and at that point you choose your new 140 and the relink is done.
By the way, there is no fax# for sending in the relink request. You have to send out a letter giving out the details and requesting for relink. In fact, that is the major problem in relinking. You just send out the postal mail/fedex and nothing happens after that. There is documented evidence including my case (and many others in this thread) that even after 6 months nothing much happens. You cannot call and find out the status. Simply put, it is a black hole. There is NOTHING that you can do to check the status or to ensure that it happens. I have a feeling that since it is a non-routine thing (relinking), they put it under "problem file" and it sleeps there..
You are relinking presumably to save time and so I sending the letter to a black hole does not serve the purpose. Research the forums, consult the lawyer and then decide.
Good luck.
Ela