Pursue with removing the cable connection of the speaker with the motherboard.

Then you can easily take the speakers off.

Grap your new speakers and reverse the last two steps.

As it is shown in the picture, the circles show thee spots where later there will be screws. you have to make sure that the speaker wire is in the provided path and not covering any of the holes. this can result in you scrawling over the wires if it is not secured properly.