-w and -h cannot be used simultaneously. Only one of the resizing methods can active. If you want to specify both dimensions, use -^XxY if you want to resize to given size ignoring aspect ratio. Or -fXxY if you want to specify maximum values for each direction and keep aspect ratio.
To specify output folder, use the -c switch + a parameter in quotes.
If you are using VB, the line could look like this:
Params = "-o -q100 -^"+widthbewerk+"x"+heightbewerk+ " -c""C:\myoutputfolder\<PATH><NAME>.jpg"" " +afbeeldingbewerk
Perhaps you'll need to escape the " and \ characters in a different way. Using extra double quotes around the input folder would be a good idea as well.