First, create a backup!!
Open up ArcMap, ensure the Spatial Adjustment toolbar is turned on and add some data that you trust to be in the correct location and with some identifiable similarities (Orthophotograpy is good, roads or parcel information can also be helpful)
Using the Spatial Adjustment Toolbar add some displacement links from-to (from where the data is to where it should really be) - add quite a few and concentrate on the edges of your data but don't forget the middle. The amount of displacement links depend on your adjustment method, how good your data is and your expectation of the results; a simple affine can be done with only 4 widely spread links and can become confused with too many (more than 20) but a rubber sheet works best with a lot of links fairly evenly distributed (but don't make them too close)..
Choose an adjustment method; Affine should be all that's required for a straight scale 'n rotate, if the data is essentially correct and in the same spatial reference but in the wrong location. Data digitized in a different or unknown spatial reference may need a higher order transformation or rubber sheet if the data is really bad or originally inaccurate.
Open up the links table and have a look at the links with really bad RMS (root mean square) - perhaps you've snapped to the wrong end of a feature. Because you've added heaps of links you can delete the really bad ones and still have enough. Preview the transformation as you go to assure yourself the result will be suitable.
If you have to do this for a few datasets you can save the links ready to reload for the next feature class. Note you can operate on all features loaded into ArcMap but may want to do this on a few computers at once - you can share the file around to help.
Now that you're happy with the parameters and links (you should also have a backup of the original and links just in case) you can perform the transformation - this used to take an extrordinarially long time but now it's not too bad.
If you notice after transforming that there's an area (or two) that could have been better you can go back to your backup, load your links and add a few more to pin down the last little bits...