xml convertor to differnet xml format

If you're talking about the tag names, it'd be easer to change the code in showfeed.brs to match your xml rather than 'converting' existing xml every time it downloads.
The Videoplayer sample SDK has showfeed.brs

        'fetch all values from the xml for the current show
        item.hdImg            = validstr(curShow@hdImg) 
        item.sdImg            = validstr(curShow@sdImg) 
        item.ContentId        = validstr(curShow.contentId.GetText()) 
        item.Title            = validstr(curShow.title.GetText()) 
        item.Description      = validstr(curShow.description.GetText()) 
        item.ContentType      = validstr(curShow.contentType.GetText())
        item.ContentQuality   = validstr(curShow.contentQuality.GetText())
        item.Synopsis         = validstr(curShow.synopsis.GetText())
        item.Genre            = validstr(curShow.genres.GetText())
        item.Runtime          = validstr(curShow.runtime.GetText())
        item.HDBifUrl         = validstr(curShow.hdBifUrl.GetText())
        item.SDBifUrl         = validstr(curShow.sdBifUrl.GetText())
        item.StreamFormat = validstr(curShow.streamFormat.GetText())
        if item.StreamFormat = "" then  'set default streamFormat to mp4 if doesn't exist in xml
            item.StreamFormat = "mp4"
        endif

my xml is starting with
<rsp>
<code id="1">
<channelList>

in videoplayer its <feed>
<endIndex>4</endIndex>
<item

my xml is looks like this,
<rsp>
<code id="1">
<channelList>
<channel id="2004" ContentType="episode" SDPosterUrl="http://downhillmoney.com/wp-content/uploads/2014/04/video-to-promote-yourself.jpg" HDPosterUrl="http://downhillmoney.com/wp-content/uploads/2014/04/video-to-promote-yourself.jpg" ShortDescriptionLine1="video garden" Description="video garden" Title="video garden" urls="http://techslides.com/demos/sample-videos/small.mp4" bannerad="" isPreroll="0" SDTickerUrl="http://ex.InstantTvChannel.com/ad-sd-g.png" HDTickerUrl="http://ex.InstantTvChannel.com/ad-hd-g.png" isTickerShow="0" isWaterMark="0" isCustomPlayer="0" waterMarkTime="837" Packid="545" Userid="" isUserLog="0"/>
</channelList>
</code>
</rsp>

Do you know any other ways, other than editing show feed.brs file.
Any software that can change my XML tag to the supported XML tag?

Notepad would allow you to open the xml file and do a search/replace -- or you could do that with the search/replace function in generalutils.brs before you parse the xml.
Note - string replacement can be extremely slow on roku with a large xml or json file as your source.

from generalutils.brs

'******************************************************
'Replace substrings in a string. Return new string
'******************************************************
Function strReplace(basestr As String,oldsub As String,newsub As String) As String
	newstr=""
	i=1
	While i<=Len(basestr)
		x=Instr(i,basestr,oldsub)
		If x=0
			newstr=newstr+MID(basestr,i)
			Exit While
		End If
		If x>i
			newstr=newstr+MID(basestr,i,x-i)
			i=x
		End If
		newstr=newstr+newsub
		i=i+Len(oldsub)
	End While
	Return newstr
End Function

basestr would be rsp, or your downloaded xml prior to parsexml. NewSub would be what you need the tag name to be, oldsub would be what the tag name is now (when you download it)