1- Open inkscape.
2- Import your image File > Import.
3- A new box will appear. ensure you have embedded selected then click ok.
4- Select your image. On the top toolbar you can see the height and width measurements. Ensure the lock is on to ensure aspect ratio.
5- Type in the height or width. with the aspect ratio locked one measurement will automatically adjust the other.
6- Another way to adjust your image is to use the arrows. select your image.
7- The arrows will appear. select the arrow you like to adjust and that will resize that side. If you want to keep the aspect ratio, hold shift key while moving the arrow.