is there a vesa bracket? how to install?

Dear, Here is the detail steps to install the vesa, and bracket will also come in the package.

How can I switch and expand the storage? any detail steps?

Dear, here is the detail to expand the storage. Hope it's helpful for you.

What is the little switch on the top of the side with the power plug opening?

After you remove the small screw the little switch is used to open the cover to install a second SSD. Easy install.

What is the maximum size hard drive it can support? Is the wifi card upgradable?

The specs listed on the Amazon page say: "(Support up to 2TB of 2.5in SATA3 SSD 2280, not included)" - However, I doubt that the Maximum hard drive "size" of the optional "add in" or "expansion" 2.5" drive would be limited really, if by "size" you mean "Capacity". The largest sizes commonly available nowadays are maybe up to 8TB in an SSD 2.5" SATA3 form factor. . ...These listings for these Mini PC's seem to change often in regards to the HDD size, CPU & amount of Ram etc. ...But mine came with 12GB Ram & a boot drive on my unit of 119gb M.2 SSD. ...The current listing says boot drive of "512GB SSD M.2" & 16GB Ram. ...But I think you would most likely have no problems adding in a drive with up to even 8TB capacity if you have the cash for it. There are even now 100TB SSD's out there but you need about $40,000.00 to own one! ...In the 2.5" form factor currently though as a second drive etc., I don't THINK there are any limiting factors as far as capacity goes unless some motherboards limit this that I'm not aware of. Of course it needs to be in the 2.5" form factor for the "Add In" expansion SSD drive. 1 or 2TB would be a nice place to start I'd think since they are pretty affordable & the specs DO say it takes up to that size for sure. - I would recommend choosing a good fast external USB WiFi adapter to upgrade the WiFi. ....The WiFi card & the boot M.2 drive on these are difficult to get to in order to change/upgrade without really tearing the whole thing apart on these little units. If you want to do stuff like that, you should maybe just get a case & build your own PC. I hope this helps you.

Max Screen Resolution	3840 x 2160 pixels
Processor	2 GHz others
RAM	16 GB DDR4
Hard Drive	512 GB
Chipset Brand	Intel
Card Description	Integrated
Graphics Card Ram Size	512 GB
Wireless Type	802.11a/b/g/n/ac
Number of USB 2.0 Ports	2
Brand	KAMRUI
Series	GK3PRO
Item model number	GK3PRO
Hardware Platform	PC
Operating System	Windows 11 Pro
Item Weight	13.6 ounces
Product Dimensions	2.03 x 5.04 x 5.04 inches
Item Dimensions LxWxH	2.03 x 5.04 x 5.04 inches
Color	Silver
Processor Brand	Intel
Number of Processors	4
Computer Memory Type	DDR4 SDRAM
Flash Memory Size	16 GB
Hard Drive Interface	SSA
Hard Drive Rotational Speed	7200 RPM
Power Source	DC
Voltage	3.6 Volts (DC)

KAMRUIMini PC,16GB RAM 512GB SSD Intel 11th Celeron N5105 (up to 2.9GHz) Mini Desktop Computer, 2.4G/5G WiFi, BT4.2, Small Computer Support 4K UHD VESA Gigabit Ethernet for Home/Business

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