What should I do about my TV aerial?

We switch over to digital in my region in less than 100 days and I've still not got it sorted. I did get a freeview box and found that sometimes I could get a perfect picture on the digital channels but sometimes I got no signal at all. I've got a set-top aerial and an external ariel but the external aerial seems to have been knocked out of position. It is on a pole attached to the wall but I think the pole has slid down. In addition, the aerial used to move around in the wind and now it seems to have got stuck in one position (pointing in a different way from other aerials nearby.) I think the aerial is probably about 17 years old (although I don't know for certain). Do I need to get a Registered Digital Installer to sort this out for me? How do I know whether my current aerial will be okay once it is back in the right position? A lot of aerial installers mention that you need a 'digital' aerial but I've heard that there is no such thing and I'm worried that whoever I employ will spin me line about needing a new aerial in order to get more money out of me and I don't know enough to know whether to believe them or not. My flat is 3 floors up so, unless they can adjust the aerial from a window (which they may be able to do), is it going to be difficult/expensive to get someone to do this? Could they use a ladder or would they need to erect scaffolding? I was thinking of just getting the aerial adjusted and then seeing whether it works or not but, if I then have problems and do need a new aerial, I could potentially end up paying a lot of money twice, if getting someone to work at that height is difficult and expensive. Can anyone please advise me?