Electrical – Add LEDs to ceiling fan

The simplist solution is to replace the fan/light combinations with modern units that have wireless remote controls for both light and fan, and include multispeed settings for the fan.

Your current setup probably has a direct hot connection to the fan with a single pair of hot wires going to the switch for the light. This switch could be converted to turn the fan and light on or off together, but not separately without running additional wires.

You could snake new wires in to have separare controls for fan and light (a cable with three wires would do with a double switch), but this is requires routing cables through the walls and patching the plaster/wallboard after installation.

This also would not give you three speed controls at the wall. The three speed switches in most fans (those that use pull chains instead of a wireless remotes) cannot easily be controlled by a wall switch without a significant change in internal wiring, not a job for a novice.

A retro conversion could be done, but a replacement may be easier and maybe even cheaper than hiring an electrician to do the rewiring (remote fan/light combos can be had for less than $100).

If you're looking to add a light to an existing ceiling fan, making it a combination fan/light, this will only work if (1) the fan is designed to accept an optional light add-on and (2) you use the light add-on appropriate to your fan. If you don't know what type of fan you have, this will be difficult to find, but you could start by turning off the power and seeing if you can detach a part on the bottom of the fan. If this reveals some wires or wiring terminals you may be in luck; measure any attachment points and look for an add-on from the same manufacturer that would fit.

If you're talking about just swapping out the whole fixture, you could relatively easily replace the existing ceiling fans or light fixtures with new fans or fixtures. Most fixtures are designed to attach to standard ceiling boxes. These sorts of changes can also be easily undone (remove your new fixture and reattach the old one) if needed, which may be useful in your situation. Note that if you're attaching a ceiling fan, you need to be sure the box you're attaching to is rated for fan use (i.e. has a stronger attachment to framing to support the weight/motion of the fan).