$text = 'here is some text with Uppercase letters'
 
$c = 0
$position = foreach ($character in $text.ToCharArray())
{
 $c++
 if ([Char]::IsUpper($character))
 {
  $c
  break
 }
}
 
if ($position -eq $null)
{
 'No uppercase characters detected.'
}
else
{
 "First uppercase character at position $position"
 $text.Substring(0, $position) + "" + $text.Substring($position)
}

PS C:\&;First uppercase character at position 24
 here is some text with U