how to change size of a photo

Hallo, ich würde es in Photoshop auf die gewünschte Größe skalieren und dann nach Illustrator exportieren oder über kopieren/einfügen übertragen.  Ich hoffe, dieser Vorschlag hilft Ihnen weiter.

Hi @kalle_9677,

I hope that the expert's suggestion about showing the bounding box helped you resize your photo to fit the artboard. Are you still facing any issues with this? Please let me know how it's going. Also, could you share which version of Illustrator you’re using and the details of your operating system?

Looking forward to your update!

Abhishek 

Probably the bounding box is turned off.

Go to View > Show bounding box and try again.

You have to use the Selection tool (black arrow)