Morning to you.
This is a bit of a long story - have a look at this link
astra2d.co.uk
It explains what has recently happened with the BBC moving over to the Astra 2D satellite, and will give you information as to how to get your BBC channels back.
There isn't a need to re-align your dish to pick up 2D, this satellite is part of a cluster of satellites, all positioned at 28.2 degree. The 2D satellite has a smaller footprint (coverage area) then the other Astra 2 satelittes, and you are now on the edge of the footprint, and consequently the signal you are receiving is weaker.
A lot of the other members here will be able to advise you as to whether you may have to change some components of your system, but you will need to post details of your equipment, i.e.
size of dish
type of lnb
digibox manufacturer and model ref
Hope this has helped
richardinalex