Should I increase weight?

[SCPrl]

I use to lift five pound dumbbells, and for the past half year or so I've been lifting ten pound dumbbells, but I'm not sure how much effect it's having anymore. I sometimes find that I'm doing more reps than I intended to do without even noticing. I can still only do ten lateral deltoid raises with ten pound weights, but more than 30 of everything else.

Should I switch to fifteen pound dumbbells if I want to increase strength?
If so, is it okay to stick with ten pounds for lateral deltoid raises?

[SCPrl]

Cool beans. Thank you. Your advice in this thread, as well as other one, has been very helpful. =]