Haven't blended my beer, but I have blended some of my meads. The meads, being still, presented less of a challenge. Assuming your beer is finished & carbonated, it's a bit more difficult. But basic procedure would be the same.
You want to start at your bar or kitchen table with the base beers, a measuring cup or cylinder, and a bunch of glasses. Blend in varying, carefully measured proportions and do some comparative tasting until you get the mix right to your taste. You could then fill a keg with the selected proportions of the two (or more) beers, carbonate and you're ready to serve from the keg or fill bottles as desired.