Fixing poorly applied stickers
Unfortunately older stickers are difficult to remove and reapply because the sticky part of the paper tend to rip off and leave a residue on the LEGO element itself. But the fact of the matter is that applying that taking off and re-applying even a new sticker is a challenge and it will almost always be visibly damaged at least a little bit. 

Your best bet is just to get new stickers. You can find pretty much any sticker-sheet LEGO ever released all the way back from the beginning, and many times in new condition. In fact several Bricklink stores specialize in selling old stickers. 

Just go to Bricklink, type in the set number and look at the inventory listing. The sticker sheet will be included there. Then see which seller have it at what prices and choose the one you like the most. 

Here is the general listing of all LEGO stickers: http://www.bricklink.com/catalogList.asp?catType=P&amp;catString=160