As Sam has already said, desoldering the old caps can be difficult. Snipping them off and soldering the new one to the remains of the old leads is certainly an option and will avoid damage to the valve holders.
If you are going to take up radio restoration as a hobby you might like to think of getting a desoldering station at some point. I struggled for years using solder wick and deslodering pumps then eventually bought one of these
http://cpc.farnell.com/duratool/d006...BoCrfwQAvD_BwE
They are quite expensive but they do make the job very much easier and I wouldn't be without mine now. Something for a future Christmas present maybe?