Starting with some basics for beginners, hope some of this is helpful! This is my first tutorial, so bare with me...
First, open your image in PSP
Select the layer you want to resize on your layers palette.
Now go to Image-->Resize
A box will pop up like this one: (make sure to click on "advanced settings")
You can resize in pixels or percent, I use percent.
You may need to resize, then if it is not the size you want, undo it and try again until it is the size you need.
I have found that using "smart size" gives the best picture.
If you are resizing just one element, make sure the box for "resize all layers" is unchecked.
If you are resizing a whole template or siggy, check that box.
Like I said, you may need to play around with the percentage or pixel dimensions to get the size you want, it is best to undo and try again. If you resize too much without undoing, it will distort your image.
Hope this was helpful!