I have a Lenovo IdeaCentre 300s-08IHH desktop that I'm trying to upgrade the graphics card on and possibly the power supply. I wanted to upgrade the card for better picture quality and to use multiple monitors and maybe some light gaming. The problem is I'm not sure what one would be the best or what options I have as far as the graphics card and power supply. The power supply is small and there are wires running over the PCI e slot.  Is it possible to upgrade the graphics card without upgrading the power supply? If not, what power supply and graphics card do recommend? 

• Windows 10 Home 64 bit
• Intel Core i5-4460s 2.9 GHz Processor
• 8 GB  DDR3 RAM (upgrading to 16 gb)
• 1 TB 7200 rpm Hard Drive

Hey, I also have the same PC and I’m also not sure what graphics card fit.

I’ve been researching and you can only fit Low Profile video cards.

https://www.amazon.com/gp/product/B06WWLWWJM/ref=ox_sc_saved_title_1?smid=ATVPDKIKX0DER&psc=1&tag=linus21-20 

Like this ^ 

I asked a person online if they bought the graphics card for the same computers we have. 

Have to wait until someone helps..

Did you see this thread?  Can-I-change-the-graphics-card-on-IdeaCentre-300s

What is the best processor that this model supports. I7 4790s or I7 4790. In its spec sheet, its mentioned 4790s but i guess that is due to PSU limitations of 180w. Will it support 4790 desktop processor if i don’t want to add any graphic card or any other power hungry equipments.

Officially, only the i7-4790S is supported, and it is not only power dependent. 

The cpu microcode in the BIOS must also recognize the 4790 -- it may use the same as the 4790S, but that is not a given.  And the CPU cooler must be a 95w part.  The parts list for your system shows both 65w and 65/95w parts.  You would need to determine which part you have, and upgrade if necessary. 

https://pcsupport.lenovo.com/us/en/products/desktops-and-all-in-ones/300-series/300s-08ihh/90f1/parts/display/compatible