How often do I need my coolant flushed?

I have a 1993 ford ranger.

Will be in ford service manual recommended changes.

Every 3-5 years. 3 is better. Drain and refill is fine. Flushing doesn't hurt but with frequent changes, which I would suggest, drain and refill is plenty. The advantage of frequent changes is to prevent internal rust for less overheats. Which are much more likely to leave you stranded or destroy your engine than anything that might happen with motor oil. If you do overheat, stop driving immediately, get a tow if you don't know how to wrench it, and as the first thing to try replace the thermostat with a factory thermostat.

For recommended maintenance frequency on this and other items check the manual. Do everything.

You really should check your owner's manual and go by what it says. You don't want to put in the wrong type of antifreeze for your car. Also, it will also tell you how often to change your coolant.

If you're asking the question about changing as well as flushing, I suggest not using the all too common ethylene glycol - instead use Propylene Glycol because it is non-toxic, non-lethal and lasts longer. In some cases the label or brand should state the specs but if not every couple years should keep everything in good running order.