Unfortunately you can't upgrade the fan. If there is a heat problem you can replace the fan and change the thermal paste onthe CPU and for a big amount of time your computer will run in lower temperatures.
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It will be difficult to find another fan that it will be better and suitable for the laptop. To find a better fan you should check to find fan at the same exact size, same voltage same amp but more RPM. That of course it will cost you battery life and honestly i don't think that you can find another fan suitable except from it's own.
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If there is a heat problem you can replace the fan and change the thermal paste on the CPU and for a big amount of time your computer will run in lower temperatures.
Unfortunately you can't upgrade the fan. If there is a heat problem you can replace the fan and change the thermal paste onthe CPU and for a big amount of time your computer will run in lower temperatures.