In Magix PhotoDesigner you go to 'Image' >> 'Scale' where you can choose either a percentage of the original size or an absolute pixel dimensions. I'd assume other Magix programs would operate similarly.
Looking at the manual for Photmanager - I cannot find any reference to resizing. The sotware is deign to locate and manage your photos with very basic image correction functions. ie
Arrange photos - find and gather photos from anywhere on your computer.
Import photos - from digital camera or scanner to your computer.
Sort photos - make photo collections as one group and categorise
Select photos - eg, all images showing a certain person
Retouch & restore photos - straighten crooked photos, red eyes can be removed with a click.
Present photos - photos can be collected in a playable photo album and presented in full-screen.
You need to use an image editing program to do anymore then the basics offered by Photo Manager