Tweak formatting, clarify language

Author: CVYY39

docs/upgrade_firmware.md

@@ -2,18 +2,17 @@
 
 The keyboard has a built-in bootloader to upgrade its firmware.
 
-## Check Current Firmware Version
+## How to Check Current Firmware Version
 
-To check the information of the firmware, just open the `boot_out.txt` file in the USB storage of the keyboard. The file contains the version and the compiled date of the firmware:
+To check the current version of the firmware, just open `boot_out.txt` in the USB storage device of the keyboard. This file contains the version number and the compiled date of the firmware, for example:
 
 ```
 Adafruit CircuitPython 6.0.0-alpha.1-110-g121d78ec9 on 2020-08-27; Makerdiary M60 Keyboard with nRF52840
 ```
 
-If you find a newer firmware (file with `.uf2` extension) in [python-keyboard / firmware](https://github.com/makerdiary/python-keyboard/tree/zh-cn/firmware), you could do an upgrade.
+If you there is a newer firmware (file with `.uf2` extension) in [python-keyboard / firmware](https://github.com/makerdiary/python-keyboard/tree/zh-cn/firmware), you can do an upgrade.
 
-
-## Enter Bootloader
+## How to Enter the Bootloader
 
 There are 4 ways to run into the bootloader:
 
@@ -31,7 +30,7 @@ There are 4 ways to run into the bootloader:
 
 4.  When battery is not attached, hold the ON/OFF button and power on the keyboard with USB.
 
-## Upgrade
+## How to Upgrade
 
 When the bootloader is running, a USB drive named `M60Keyboard` will appear in your computer.
-Download the latest `.uf2` firmware, drag-n-drop the firmware into the USB drive, then wait until a new USB drive named `CIRCUITPY` appears.
+Download the latest `.uf2` firmware, drag-n-drop the firmware into the USB drive, and then wait until a new USB drive named `CIRCUITPY` appears.