The new ribbon is live (sort of)

When you update your Power BI application, the following message should appear: 

Click on the link to see more information about the new ribbon (or failing that, click here).  The ribbon is actually still in preview mode, but the option is now turned on by default.

A summary of the new ribbon

Here are what the main ribbons look like:

The main new ribbons.

There's also a new look to Power BI too (less yellow, more monochrome):

It's all familiar, but not the same - the colours seem to have been muted a bit.

Collapsing the ribbon

A nice idea is that you can collapse the ribbon to make it take up less space (here it's collapsed to a single row):

Click on this arrow at the top right of Power BI to collapse (or expand) the ribbon.

This will toggle your view of the ribbon:

Here we've reverted to the full ribbon.

Custom number formats

My favourite new feature of the ribbon is that you can now type custom number formats into a sensible place:

If you want a column or measure to appear with a custom number format, you can type this into the Format box (although nothing tells you that you can do this!).

Dynamic context

The ribbon now reflects what you're doing - so (for example) if I've got a measure selected I see everything that I could do with measures:

The Measure tools part of the ribbon.

But if, conversely, I've got a calculated column selected, I see a different ribbon:

The Column tools part of the ribbon.

All very slick, and it makes Power BI easier to use (which can only be a good thing).

Keyboard short-cuts

You can now press Alt in combination with the Windows key to use short-cut keys:

Hold down the Alt key and press the Windows key to enter accessibility mode.

Now you just have to learn all of the letters!

The Home tab menu in accessibility mode.

Removing the new ribbon from preview

Technically the new ribbon isn't live yet.  What Microsoft have sneakily done is to enable its preview.  To undo this, select this option:

Select to change your options and settings.

Now untick this box:

Untick the box to turn off the updated ribbon.

You'll need to restart Power BI to see the effect.