A desktop computer is a personal computer that is designed to be used at a single location and typically connected to a separate monitor, keyboard, and mouse. It is different from a laptop in that it does not have the portability of its counterpart.

When choosing a monitor, consider factors such as screen size, resolution, panel type, refresh rate, and ports. Larger screens will offer more space to work on and a higher resolution will give you sharper images. IPS panels are known for offering better image quality and a wider viewing angle compared to TN panels. Refresh rate is important if you play games or watch movies since it determines how smooth they look. Lastly, make sure the display has the port types of your PC can support.

Yes - depending on the model certain hardware components like RAM hard disk drive solid state drive etc. can often be replaced without too much difficulty. However, heavier upgrades such as replacing graphics cards, motherboards processors etc. may require more effort and special tools so it's always best to contact local IT professionals prior attempting these tasks.