How can Increase the height of Jivelite in pCP

[diode84]

Hello
I am running pCP7 on a Pi 3B+ into a 7 inch screen 1024 x 600. I would like to increase the height as there is a 1 cm border at top and bottom of screen. I am using HD 640 x 480 skin.
I have tried altering config.txt to:
overscan_top=-100
overscan_bottom=-100
(Thanks to Chill)
This does reduce the top and bottom border but only in the pCP boot up screen, not in Jivelite.
Is there any way I can do this in Jivelite.
Help appreciated
Thanks
diode84

[paul-]

You can define the frame buffer size on the tweaks page, but AFAIK, there is no way to upscale a skin.

[diode84]

You can define the frame buffer size on the tweaks page, but AFAIK, there is no way to upscale a skin.

Thanks but what is the frame buffer size and what does upscale a skin mean.