I'm not sure..... I had the whole column out and in bits then put it back together again as I replaced the bottom collar also. You might just be able to do the top bush through taking the streering wheel off and then keeping going spdown the layers. The Bentley manual will tell you the steps, definitely recommend one.
In taking it apart, I also found that the rubber connection to the steering box was cracked, and that the bolt on the column to steering box wasn't tight enough (and so there was some play on the splines). I have to say, if it's old and you've never had it in bits, then take it to bits, replace and refurbish then put it back together again. Fill your box steering box with the oil of your choice and generally give it all a bit of love. For the cost of the bits of plastic and rubber and a small bearing you might as well do a proper job.