Dlsr low filter bypass replacement, what's it involve?

I bought a used nikon d50 very cheap ( i know ) its been great but i took a shot of a light coloured subject f22 and upon upload to computer i notice lines running through the image.
i took a few white sheet photo tests and you can clearly see these lines at apetures f22, being a newbie dslr person i did not think to test to this level and the screens are not the best on these anyway.

Does this also happen when the lens aperture is at say f/5.6?

It could be that someone attempted to "clean" the sensor by rubbing it with something, causing streaks on the low bypass filter covering the sensor. Replacing the filter can be done here.

http://shop.lifepixel.com/5-Scratched-sensor-filter-replacement-service/Scratched-sensor-filter-replacement-service-p64.html

Lines (of different colours) running through the image can also mean that the sensor is bad and it needs replacing. This can cost a lot more than the camera may be worth to repair.

I very much doubt you would be able to replace the filter yourself. That sounds like a Nikon service job to me - and any Nikon servicing is going to cost more than an old D50 body is worth. Probably cheaper and better to pick up another D50 or D70 secondhand - or a D40 or D60 if you don't have the older AF-D lenses.