arrange vector in descending order
I guess that what you want is a descending sort algorithm, but in the case of Fibonacci numbers you can take advantage that they are already sorted at the beginning. Here are different strategies that you can try :

/*
  SORTING IN DESCENDING ORDER
*/

const int nbElem = 15; // 24 max
int fibonacci[ nbElem ] = { 0, 1 };

void createFibonacciArray( int inputArray[], int arraySize )
{
  fibonacci[ 0 ] = 0;
  fibonacci[ 1 ] = 1;
  for( int i=0; i&lt;nbElem-2; i++ )
    fibonacci[ i+2 ] = fibonacci[ i ] + fibonacci[ i+1 ];
}

void displayArray( int inputArray[], int arraySize )
{
  for( int i=0; i&lt;arraySize; i++ )
    Serial.println( inputArray[ i ] );
}

void displayArrayReverse( int inputArray[], int arraySize )
{
  for( int i=arraySize-1; i&gt;=0; i-- )
    Serial.println( inputArray[ i ] );
}

void reverseArray( int inputArray[], int arraySize )
{
  for( int i=0; i&lt;nbElem/2; i++ )
  {
    int fTemp = fibonacci[ i ];
    fibonacci[ i ] = fibonacci[ nbElem-i-1 ];
    fibonacci[ nbElem-i-1 ] = fTemp;
  }
}

void inverseBubbleSort( int inputArray[], int arraySize )
{
  for( int i=0; i&lt;arraySize-1; i++ )
  {
    for( int j=0; j&lt;arraySize-1-i; j++ )
    {
      if( inputArray[ j ] &lt; inputArray[ j+1 ] )
      {
        int temp = inputArray[ j+1 ];
        inputArray[ j+1 ] = inputArray[ j ];
        inputArray[ j ] = temp;
      }
    }
  }
}

void bubbleSort( int inputArray[], int arraySize )
{
  for( int i=0; i&lt;arraySize-1; i++ )
  {
    for( int j=0; j&lt;arraySize-1-i; j++ )
    {
      if( inputArray[ j ] &gt; inputArray[ j+1 ] )
      {
        int temp = inputArray[ j+1 ];
        inputArray[ j+1 ] = inputArray[ j ];
        inputArray[ j ] = temp;
      }
    }
  }
}

void setup()
{
  Serial.begin( 115200 );

  // Create and display Fibonacci array
  createFibonacciArray( fibonacci, nbElem );
  Serial.print( "\n\nFIBONACCI ARRAY\n" );
  Serial.print( "===============\n" );
  displayArray( fibonacci, nbElem );

  // Solution 1: Display array starting from the end
  Serial.print( "\n\nFIBONACCI ARRAY STARTING FROM THE END\n" );
  Serial.print( "=====================================\n" );
  displayArrayReverse( fibonacci, nbElem );

  // Solution 2: Reverse array
  reverseArray( fibonacci, nbElem );
  Serial.print( "\n\nFIBONACCI REVERSED ARRAY\n" );
  Serial.print( "========================\n" );
  displayArray( fibonacci, nbElem );

  // Solution 3: Inverse bubble sort array
  createFibonacciArray( fibonacci, nbElem );
  inverseBubbleSort( fibonacci, nbElem );
  Serial.print( "\n\nFIBONACCI SORTED IN DESCENDED ORDER WITH BUBBLE SORT\n" );
  Serial.print( "====================================================\n" );
  displayArray( fibonacci, nbElem );

  // Ascending order sort array
  bubbleSort( fibonacci, nbElem );
  Serial.print( "\n\nFIBONACCI SORTED WITH BUBBLE SORT\n" );
  Serial.print( "=================================\n" );
  displayArray( fibonacci, nbElem );
}

void loop()
{}