I would suggest doing some cardiovascular workouts in addition to weight training. You should do a circuit weight training program too since you want to lose weight, plus the circuit will give you that resistance training you want. Just to note, it's not "toning." In literal sense, toning is nothing more than making your body able to ... flex lol (substaining a contraction is tonus, and being able to return back to normal means you're toned pretty much)

As for finding out what reps and sets you should do. Start off light. If you do a circuit, you'll want your upper body routines to generally tire you out at about 12-18 reps, and your leg workouts anywhere from 15-24. So do the different machines you have there and find out what weight it takes for you to get a good burn and get fatigued by so you can't lift much more within those rep ranges I gave. Now if you don't know what a circuit is, basically you use a machine for say 35 seconds, then you take 15 seconds to rest and be on something like a bike or do a jog and do that for 35 seconds, then another 15 second interval of recovery and you go back to a machine. There's many ways you can do this. The idea is to do a resistance training, then do a cardio something (bike, run, situps, jumping jacks, whatever comes to mind, etc).

The basic circut is weight to bike to weight to bike. You could also do something we call a "big five" where you do weight, weight, weight, weight, weight, then bike for the equivelent of time (still doing the activity for 35 seconds and 15 second intervals). This is the best thing for beginners (or returning from a long rest period after a marathon ... like me lol). This will give you great resistance training depending on how hard you want to go in it. Plus it gives you an awesome cardio (if you push yourself especially) which will help you burn fat. So it's the best of both worlds really.

And when do you increase the weight? As you become stronger your body will adapt to dealing with the resistance variable you have (which is the selected weight you've found), as it becomes easier and you can complete the say 15 reps in that 35 seconds and you're not tired ... increase the weight! Your goal is to strain to lift up that 15 reps.

Another big thing to look at, especially if you don't have a specific circuit class, is to what order you do the machines in. I can't give any order you should, but you don't ever want to hit the same muscle twice in a row, and you want to keep the big muscle machines separated well in this routine so you don't hit say leg press, abs, squat! Your legs will be dead after being fatigued not too long ago. But it is good to have opposite muscles close together or right after each other, say a leg press and then a leg curl (first works quads, and the other hamstrings - agonist vs antagonist).

And you should be able to do a circuit in 45 min say. So it's a good duration, your intensity and overload is dependant on how much you want to lift on each station and how hard you push yourself in the cardio aspects (as I have a cardio class after my circuit class I don't go very hard on the bikes, but sometimes I'll do sprints). The good thing about this is you can change it up (variability) by either how you go about doing the machines (and if there's no set design, you can really change it up, but you better preplan the orintation of how you go around to the different stations) or you can change what cardio aspect you're doing.