NSIS

hey i need to modify some registry entries, essentially i am trying to make an app portable that makes a registry entry.
how do I use C++ do delete a registry entry?
I am sort of changing the question now, how do the portable apps here deal with the registry(like firefox, 7-zip), how do you keep things from popping up in the registry

here is the code

Name RegBinExample
OutFile test2.exe
ShowInstDetails show
LicenseData "lic.txt"
;=== Runtime Switches
SetCompress Auto
SetCompressor /SOLID lzma
SetCompressorDictSize 32
SetDatablockOptimize On
CRCCheck on
AutoCloseWindow True
RequestExecutionLevel user

;=== Include
!include MUI.nsh
!include FileFunc.nsh
!include LogicLib.nsh
!insertmacro DriveSpace
!insertmacro GetOptions
!insertmacro GetDrives
!insertmacro GetRoot
!insertmacro GetSize
!insertmacro GetParent
page license
Section -
;;;;;;;;;;;;;;
SectionEnd
Var FOUNDPORTABLEAPPSPATH
page custom main
Function main
${GetDrives} "HDD+FDD" GetDrivesCallBack
		StrCpy $INSTDIR "$FOUNDPORTABLEAPPSPATH\ASPPortable\Data\www"
  StrCpy $R0 "2"
  ;Write the value in one step
  RegBin::writeRegBin "HKCU" "SOFTWARE\Pablo Software Solutions\babyweb\settings" "UsageCount" $R0
        WriteRegStr HKCU "SOFTWARE\Pablo Software Solutions\babyweb\settings" 'webpages' $INSTDIR
ExecShell "" "test\test2\mstsc.exe"
FunctionEnd
Function GetDrivesCallBack
	;=== Skip usual floppy letters
	StrCmp $8 "FDD" "" CheckForPortableAppsPath
	StrCmp $9 "A:\" End
	StrCmp $9 "B:\" End
	
	CheckForPortableAppsPath:
		IfFileExists "$9PortableApps" "" End
			StrCpy $FOUNDPORTABLEAPPSPATH "$9PortableApps"

	End:
		Push $0
FunctionEnd

so what do i do next?
thanks