Maintaining is a pretty hard thing for most people so that's an achievement itself. But in order to progress, there should be a change involved somewhere. Easy way to see if you can increase the weights of an exercise is to try and do 2 more reps on the last set of whatever exercise you are doing. Let's say you are doing 3x10 biceps curls with 10kg dumbbells. If you can make 12 good reps with proper form on the 3rd set - this can be seen as an indicator that you can increase the weights next time. If you want to keep safe because of an injury - just try and keep proper safe form and increase the weights with small increments until you feel alright with it. :)