Access is denied when executing xp_cmdshell delete

hi y'all!
here i am again with another problem:

declare @.path varchar (100)
declare @.filename varchar (100)
delcare @.delete_this varchar (100)
declare @.cmd varchar (100)

set @.path = '"\\servername\shared\"'
set @.filename = 'file.txt'
set @.delete_this = @.path+@.filename
set @.cmd = 'del '+@.delete_this

exec master..xp_cmdshell @.cmd

i get this:

Access is denied.

Please Advise
Thnx.I've also heard of "net use"

Can u please enlighten me on this.