The fluid should be red and not smell burned. If the fluid is brown or smells burnt, it's time to replace it. How often to check it: Monthly. How often to replace it: This varies from car to car and depends on transmission type, but it's typically between every 50,000-100,000 miles.
http://lifehacker.com/five-fluids-you-should-check-to-keep-your-car-running-s-1556413981
How often to check it: Once a month. How often to replace it: Between 50,000 miles and never. Typically speaking, most car manuals recommend keeping the power steering fluid levels topped off, but you'll rarely need to flush and replace it. Double check your owner's manual to make sure you can ignore yours.
http://lifehacker.com/five-fluids-you-should-check-to-keep-your-car-running-s-1556413981
Should I flush transmission fluid for a Japanese car with 140K miles? How often should I change my transmission fluid? Should I change transmission (AT) fluid on a 2008 Infiniti G35xS with 79,300 miles whose transmission fluid hasn't been changed for around 35,...
https://www.quora.com/How-often-should-transmission-fluid-be-changed
How often to check it: It was once recommended that you check your oil every time you fill up with gas, but with most modern cars you're safe checking it once a month. How often to replace it: This depends on the car, manufacturer, and year. The 3,000 miles or every six months saying doesn't really apply any more.
http://lifehacker.com/five-fluids-you-should-check-to-keep-your-car-running-s-1556413981
According to the Nissan Service Manuals it is recommended you replace your CVT Transmission fluid at those intervals via a Drain/Refill. If you notice at every interval (30K, 60K, 90K and 120K), it indicates that a Flush is optional. What is basically means that its not recommend.
http://my6thgen.org/f7/when-should-i-drain-refill-flush-my-cvt-transmission-3153/
Manual: In a manual transmission, the problem is not so much the fluid degradation, but rather fluid contamination. This contamination occurs over time as the synchronizers, bearings and gears in the transmission wear out. The resulting metal particles then float around in the lubricant.
http://www.cartalk.com/content/service-your-car-14
You can check your transmission fluid the same way as your engine oil, except the car should be running when you do it. Unlike your engine oil, transmission fluid is part of a closed system, so it should never be low. If it is, take it into a mechanic. Instead of volume, you're looking at the quality of the fluid.
http://lifehacker.com/five-fluids-you-should-check-to-keep-your-car-running-s-1556413981
Most normal average daily commuters wait until 60K to replace their CVT fluids. Now those who push it every single day...30K would be a good start. Push meaning Pedal to the Metal. But before doing anything you should always check your fluid before changing it.
http://my6thgen.org/f7/when-should-i-drain-refill-flush-my-cvt-transmission-3153/
Yes, definitely, regardless of whether you have a manual or an automatic transmission. Manual: Most manufacturers recommend that manual transmission fluid be changed every 30,000 to 60,000 miles. Under heavy-duty use, some manufacturers suggest changing transmission fluid every 15,000 miles. Automatic: Service intervals for an automatic transmission vary from every 30,000 miles ... to never. The typical service interval is 60,000 to 100,000 miles.
http://www.cartalk.com/content/service-your-car-14
A lot. It's a small gesture with huge dividends. - Oberyn hates the Lannisters, so the ability to put one of them (any of them) in front of an executioner is tempting (and conveniently, it happens to be a Lannister that Tywin doesn't like or need, a small price for Oberyn's good will).
https://www.quora.com/How-often-should-transmission-fluid-be-changed
how often should transmission fluid be replaced
A  transmission fluid be replaced every 30,000 to 60,000 miles. A transmission fluid should be replaced every 30,000 to 60,000 miles.