Save File As Increment

I'm writing some VBA code for a Macro to run that will save my file in a directory using the file name from a cell. I want to be able to increment the save file name if the same file name already exisits

i.e.

If no file then save as FileName
If exists then FileNameVer2
If both exists then FileNameVer3

And so fourth (maximum iterations will be about 10)

I'm new at VBA but written some code to save

VB:
Sub SaveAs()
Dim FName As String
Dim FPath As String

FPath = "S:TestTest Directory"
FName = Sheets("Parameters").Range("B9").Text
ThisWorkbook.SaveAs FileName:=FPath & "" & FName
End Sub

At the moment I have concatenated four cells to produce the file name in B9 but if there was a way to use variables that would be awesome too!

The code runs when I press a macro button saving save, but at moment it says "file alerady exists , overwrite" when I put no, it goes to a debug.