The shears not closing correctly may have to do with a faulty hinge mechanism. Please be advised Fiskars shears come with a lifetime warranty, so it would be worth speaking with the place of purchase for advice on this issue.
If you wish to use a file, I've taken a few photos of my own shears to give a better illustration of the bevels and angles which they follow. There will be two bevels which you need to be aware of.
The first bevel:
The second bevel: This is the only one I would be sharpening on your shears. Please note the angle is much steeper than the previous bevel.
Use consistent strokes with even pressure, from the base of the blade to the tip. We won't be removing a lot of material, simply touching up the edge.
After you have sharpened this leading cutting edge bevel, flip the blade over and with one stroke remove the burr which has been created. In this case, I have also cleaned the remaining surfaces as the shears were severely neglected.
We are looking forward to seeing your shears back in action. Please feel free to ask if there is anything further you would like to know. I'd be pleased to share more details on the sharpening method or answer any questions you have.