I wanted to un-install uVision 3 for 4 because I found that it did not have support for MCBSTM32. The problem is that I cannot find ways to un-install it before installing uVision4. Pls advise. Thanks in advance
You shouldn't have to add anything - it should just be there!
If it isn't there, then you must have a really old version - so just replace it with the latest!
"Today I got the STM32 kit board for the first time. but somehow I also got CD software uV3, not 4."
As already noted, uVision3 is perfectly fine; if you really want UV4, you can download & install it separately - it won't upset the UV3 installation.
At this point, since UV4 is very new, you'd probably be best to stick with UV3 - since that will (probably) be what's in all the examples & documentation!
If you've only just got the kit, then the first thing to do is to read the manual - it will be on the CD, and is also here: http://www.keil.com/mcbstm32/
Quick Start Guide: http://www.keil.com/mcbstm32/mcbstm32_quickstart.pdf
See also: http://www.keil.com/support/man/docs/gs/
http://www.keil.com/support/man_arm.htm