I have an "Intel(R) Centrino(R) Advanced-N 6230" adapter in my notebook. I want to upgrade to an adapter with higher rate, which one is the correct adapter for replacement?
The best adapter in this form factor that you could use is the Intel Dual Band Wireless-AC 7260 Plus Bluetooth.
Here is the Intel page for this adapter: http://www.intel.com/content/www/us/en/wireless-products/dual-band-wireless-ac-7260-bluetooth.html Intel® Dual Band Wireless-AC 7260 Plus Bluetooth*
Here is the Amazon.com page for this adapter: https://www.amazon.com/Intel-Wireless-AC-Network-Bluetooth-7260-HMWWB-R/dp/B00N7474CS Amazon.com: Intel Dual Band Wireless-AC 7260 2x2 Network plus Bluetooth adapter
A word of warning: Some notebooks implement what is called a white list. That is, they will only operate if the hardware installed is included in this white list. It is a slimy method that some manufacturers use to try to force folks to purchase the hardware only through them. If your laptop's BIOS implements a white list and this AC card is not included in this list, it is not going to work.
As Scott mentioned, the Intel Dual Band Wireless-AC 7260 is an 802.11ac adapter available in PCIe Half Mini Card form factor, the same used by the Intel® Centrino® Advanced-N 6230. If you plan upgrade, we advise to contact the http://www.intel.com/content/www/us/en/support/topics/OEMs.html Computer Manufacturer Support, so they can let you know if a newer adapter is compatible with your PC.
Keep in mind that an unsupported wireless adapter may not be recognized by the computer, it may lead to system errors or connectivity problems. Installing an incompatible adapter may even damage the adapter, the PC, or both. In some countries, this may even be illegal.
For more information please check the following documents:
http://www.intel.com/content/www/us/en/support/network-and-i-o/wireless-networking/000005846.html Why Doesn't My Laptop Recognize My New Intel® Wireless Adapter?
http://www.intel.com/content/www/us/en/support/network-and-i-o/wireless-networking/000005687.html Regulatory Information Regarding Hardware Installation or Upgrade