what do you have to do ? do you just switch high beam bulbs into the low beam spots and if so do you replace the high beams with something else??

 

http://www.bmwe34.net/E34main/Upgrade/More_light.htm

 

There are LOTS of threads that will help with the specifics. But as a high-level overview:

Buy Sylvania Silverstar 9005 bulbs.
Compare their plugs to the plug of the stock low-beam bulbs.
Use a dremmel or X-Acto to remove some material from the 9005 plugs.
Install the 9005 bulbs in the low-beam sockets.

Once you have the two sets of bulvs in yout hands, you can see what you have to remove. I think one of the posts here has a picture too.

Good luck.