If you need to adjust brightness, color or remove noise, this is best done before converting to dvd-video format. To do this, you would need a capture device for your computer that lets you take the video from the VHS player and put it into an avi container file using a lossless codec like huffyUV.
That part is fairly straightforward, though it takes equipment with that capability. A high quality SVHS player is also helpful.
Once on the computer, things get more complicated, as there are many different ways to apply filters, and many different programs for this process. Any good video editor should let you apply filters and preview the effects. There are even a few free ones, like Virtualdub and AviDemux, but there are also many commercial products like Adobe Premiere Elements and Sony Vegas Movie Studio.
Capturing and applying filters isn't exactly what I would recommend as a beginner's project. You might want to contact a professional service and see what they would charge.