You may be unable to uninstall assemblies using select and delete mechanism from GAC. You will need to delete them using command prompt (manually). You will get following message:
Error: "Assembly Alachisoft.NCache.* could not be uninstalled because it is required by other application."
Workaround
Do the following to delete assemblies from GAC:
Go to command prompt.
Go to folder %windir%/assembly/GAC_MSIL/
Go to the respective assembly folder and remove the assembly.