Web deploy delete existing site in export

Hi guys;

I try ti migrate from IIS 7.5 to IIS 8.5, i installed Web deploy 3.5 and i have this command for export:

msdeploy -verb:sync -source:webserver,machineconfig32.netfxversion=2,machineconfig64.netfxversion=2,

rootwebconfig32.netfxversion=2,rootwebconfig64.netfxversion=2,includeAcls=true  -dest:package=D:\sites\server1.zip,encryptPassword=Password123

and for import:

C:\Program Files\IIS\Microsoft Web Deploy V3>msdeploy -verb:sync -dest:webserver,machineconfig32.net
fxversion=2,machineconfig64.netfxversion=2,rootwebconfig32.netfxversion=2,rootwebconfig64.netfxversi
on=2 -source:package=D:\sites\server1.zip,encryptPassword=Password123 

My problem is when I import the sites in the target server, all of my old sites and their directories are deleted. Can anyone help if a parameter was added in my command lines to block or skip it ??

thanks