I just bought a '95 318i with 115,000 miles and it my habit to change all the fluids when I buy a used car. When I researched this trans-topic it was clear to me at least that many had opinions but no one had any facts.
In my case I decided to skip changing the trans fluid because I was pretty sure that it had been done as part of the BMW maintenance or warranty claim on the trans on my car at about 60,000 miles.
The Haynes manual describes it as a pretty ordinary change except for, get the car perfectly level, and then, recheck the fluid level when the trans is warm not hot at 105 to 135 degrees. If you do a search you will get plenty of advice.
If the trans is slipping in your car, it is way too late for a fluid change to make any difference. But maybe the gear selector is a little off, so look closely at that first, from end to end. Troubleshooting hierarchy: first look at mechanical objects, second at fluids, and third at electrics.