When your dog knows the release cue and how to sit on cue, put him in a sit, turn and face him, and give him a treat. Pause, and give him another treat for staying in a sit, then release him. Gradually increase the time you wait between treats (it can help to sing the ABC’s in your head and work your way up the alphabet). If your dog gets up before the release cue, that’s ok! It just means he isn’t ready to sit for that long so you can make it easier by going back to a shorter time.
Always remember that you are dealing with a very immature young animal. Be realistic, flexible, patient and always fair during puppy training sessions. Your puppy doesn't just automatically know this stuff! It's all new to him and he is bound to have the odd slip up and mistake along the way. Don't worry about these mistakes, just move on and do your best to prevent them in the future.
It typically takes 4-6 months for a puppy to be fully house trained, but some puppies may take up to a year. Size can be a predictor. For instance, smaller breeds have smaller bladders and higher metabolisms and require more frequent trips outside. Your puppy's previous living conditions are another predictor. You may find that you need to help your puppy break old habits in order to establish more desirable ones.