Don't bother with LED bulbs...
At this present moment in time you have to buy REALLY expensive LED bulbs (£150+ for a pair) to match the output of a good set of Halogen bulbs.
In most LED bulbs, the position of the LEDs is in a difference location compared to the filament in a regular halogen bulb, meaning the headlamp housing cannot reflect the LED light in the same way that it can for a halogen bulb.
The cheapest way to marginally improve the headlamps is to unscrew the internal projector units (3x torx screws) and clean the projector lens, then fit new bulbs. This will help a little bit, but you can adjust the height of the headlamps as they are set too low in most cases, meaning you can barely see anything over a certain distance.
The best solution is to buy new aftermarket "E46" projectors and install those. They are around £115 for a pair from here:
https://www.retrofitlab.com/en/aharo...-design-1.html
Buy them in "H7" format if you want to use regular halogen bulbs.
The difference in light output between these and the light output you're currently getting is immense.
Worth every penny.