Master Detail - how to change detail ContentPage in code

Hello,

I'm trying to build a slide menu in XAML using Master Detail Page. (see below)
I would like to find out how I can best switch out Detail A and Detail B pages in the Master detail in my code?
Any assistance appreciated!

Thanks!

    <?xml version="1.0" encoding="UTF-8" ?>
    <MasterDetailPage
        xmlns="http://xamarin.com/schemas/2014/forms"
        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
        x:Class="My.Shared.MasterDetailPageTest">
        <MasterDetailPage.Master>
            <ContentPage>
                <Label Text="Master"/>
            </ContentPage>
        </MasterDetailPage.Master>
        <MasterDetailPage.Detail>
            <ContentPage>
                <Label Text="Detail A"/>
            </ContentPage>
            <ContentPage>
                <Label Text="Detail B"/>
            </ContentPage>
        </MasterDetailPage.Detail>
    </MasterDetailPage>