Registered or Non registered you would have to undergo the same procedure.Personal advice is that if you actually require the entire premises then file a suit and it would take its own course minimum 20 years as the tenant would also contest up to Supreme Court.
So far as climbing up the stairs is only the problem then better course would be to sort it out amicably with the tenant PVT LTD CO and you can derive following benefits;
1.Lift could be installed at the expense of the tenant
2.You can bargain for a fair increase in rent.
3.You in this case enter with the tenant into a fresh lease and get that registered for a fixed term and if possible add a clause that the tenant would hadover the possession on such date .