managing drawings

hi. I'm new to SharePoint.

I have been using SharePoint to store the company drawings. I tried to amend a drawing (take from revision 2 to 3, for example) so I selected the file. A little screenshot appears showing the drawing - and I can see that this is the revision I wish to amend, however, when I check out and open the file....its of an earlier revision. 

I can't see how to download the correct/current revision! Am I doing something wrong? Should SharePoint be used for drawings?