Been playing for some hours now and i still don't understand the how to bring up the density in lower wealth neighbor hoods. I know parks raise the happiness/density but they always raise the wealth and i still need the lower wealth residences. SO can anyone explain to me how to increase density without raising the wealth?

Are you playing upper class, medieval Europe? You want middle class, 21st century America :P.

If I remember correctly from beta, roads raises density, happines raises wealth.

If you satisfy their needs but keep them in low value real estate (check the property value data layer) then they will increase density as their happiness increases, but if the property value is still low then they will stay low wealth. Lowering taxes encourages growth and is one way to quickly increase density.

Build more Wall-marts.