How to slightly enlarge photos without lowering dpi?

I have to submit some photos, but they want A3 size at 300 dpi, I thought I had a good enough camera, but it seems like I might not? I have a Nikon D3100. I'm taking photos on the largest setting and as RAW files, I then convert them to 16 bit TIFF with no compression (so I can edit them in paintshop pro. However when I check their size they are 300dpi, and only 15 x 10 inches (this is just about 2 inches less than A3 size) Can I somehow slightly enlarge them in paintship pro but not lower the DPI?

Added (1). Good suggestion - But if I enlarge it won't the dpi automatically decrease? It seems like it does in paint shop pro…

From what I understand about the camera you have, you shouldn't have a problem getting a decent size photo print. That being said, I can offer you some advice but only on Adobe Photoshop. I'm not sure how Paintshop Pro works but perhaps there's something similar you can do in that program.

In Photoshop, you would use the toolbar to adjust the size of the photo. When the box come sup on the screen, if I recall right, there are options to enlarge using the bi-cubic technique and a few others. These should allow you to increase the size or the photo to the amount you'd like.

Sorry, I couldn't be more specific, I don't have Photoshop on my laptop to pull up everything and be more specific.

Your camera has a 14 mp sensor and should easily produce such an image file if you have your camera set to shoot in the Large DX format (4608 x 3072 pixels).

I just tested a RAW file from an older Nikon D300 with a 12 mp sensor and was easily able to produce a TIFF file @ 300 DPI that was over 447 x 297 mm, a tiny bit larger than an A3 print. Your image files from the D3100 should perform even better.

I did this using an older version of Photoshop with no problem.

Two questions come to mind

1) how much are you cropping your original image?
2) are you able to make a slight increases in the image size without changing the DPI of 300 using PaintShop Pro?

What publication needs such large image files?

Your camera is plenty good enough to do what is needed, what may be is, that you don't have the other professional tools you need, Adobe Photoshop or Adobe Lightroom.

NOTE: When you make adjustments in Photoshop, the DPI remains the same. You can change the DPI and that will temporarily change the size of the images pixel dimensions to a smaller total number