Big renders

This might be a stupid question.... but how do I render big? Like as in big enough for me to be able to postwork without it looking pixellized (if thats even a word). Nearly everything Ive done so far has no postwork, but for maybe a spell effect or so. But my tablet is bust atm, but I can use a mouse if I get the picture big enough.

I altered the render dimensions in DAZ before but it still came out the size it is on screen, so I'm obviously missing something somewhere.