Hi @Jules61sutton, welcome to our forum!
You can change the size of the Swiftkey keyboard if you go to Settings > System > Language & Input > On-screen keyboard > Swiftkey Keyboard > Typing > Resize.
Just above the keyboard here you should see a little box with 3 lines inside of it, press and hold on this and drag it towards the top of the device and the keyboard will get bigger. When you are happy with the size, tap on "OK".
I hope that helps! 
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