How to change an Windows Image^ attribute with C++ - xaml

Question

I'm trying to change an Image that I've defined in XAML in C++.
Currently there is no reason for me not to simply define it as it is in XAML, but later on it will need to change, so I want to get that sorted now.
Anyways, here's the XAML:
<Image x:Name="playerBot"
Width="25"
Height="25"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Source="ms-appx:///Assets/Square Button.png"
Stretch="Fill"
RenderTransformOrigin="0.5,0.5">
<Image.RenderTransform>
<CompositeTransform TranslateX="0"
TranslateY="0"
Rotation="0"/>
</Image.RenderTransform>
</Image>
What I have is a class which stores position data and an Image^ for the Image^ defined in XAML.
Sprite.cpp - note that the variables have been defined fine in Sprite.h
image = Windows::ApplicationModel::Package::Current->InstalledLocation->Path + image;
auto img = ref new BitmapImage;
img->UriSource = ref new Uri(image);
m_image = ref new Image;
m_image->Source = img;
m_image->Width = m_width;
m_image->MaxWidth = m_width;
m_image->MinWidth = m_width;
m_image->Height = m_height;
m_image->MaxHeight = m_height;
m_image->MinHeight = m_height;
And finally my 2 attempts to change the Image^ defined in XAML in InGamePage.cpp:
Attempt 1:
String^ img = "Assets//Main Screen Background.png";
player = new Robot(img, 25, 25, 0, 0, 10, 0.5);
playerBot = player->getImage();
Attempt 2:
String^ img = "Assets//Main Screen Background.png";
player = new Robot(img, 25, 25, 0, 0, 10, 0.5);
playerBot->MaxWidth = player->getWidth();
playerBot->MaxHeight = player->getHeight();
playerBot->Source = ref new BitmapImage(ref new Uri(Windows::ApplicationModel::Package::Current->InstalledLocation->Path + img));
What these two methods do is either absolutely nothing (method one) or simply seem to delete the image/make it invisible (method two).
img is definitely the right file location, as I've used it in XAML earlier and it worked fine.