My DD is currently waking up earlier and earlier as it gets lighter. We put in a blackout blind a couple of days ago, which seems to have improved day time naps, but she is still waking up with the dawn.
As the nights get shorter, I suspect that she'll want to get up earlier and earlier. She's not too bad at calling for us to come get her yet, and plays with her toys for a while, but she still cries out for us to come and get her earlier than would be ideal.
If she's older than 2, you could try a gro clock or similar. Ds is 2.5 and began waking at 6am when previously he'd been sleeping unil 7.30ish. He is in a cot bed so would come into our room. Someone recommended a gro clock and I was a bit dubious, but within a week ds was staying in his room until 7 and now we can set it for 7.30. He loves his special clock and now proudly comes into our room and announces "the sun's out!" Seriously, it's brilliant and I can't recommend it enough for toddlers.
As requested, more details. DD is 13 months, and over winter months had been sleeping until on average 6.30 (sometimes 6, sometimes if we were lucky 7). She's now shifted to, typically, 5.30.
She is in a cotbed, with soft toys at one end that she plays with when she first wakes.
She had been in a baby sleeping bag, with a blanket over when it was cold, but we tried just the blanket and it doesn't seem to have made much difference.
She consistently sleeps through the night, with a bed time around 7 and self-soothes. In fact, in the evening she doesn't like to be cuddled too much, and prefers to 'do it herself' so to speak. When she wakes in the night she seems to understand that it is still time for sleep, so will go back to sleep, occassionally with a little wimper but often not.
The alternative, rather than dropping a day-time nap, would be to try and push her bed time a little later (only move by ten mins or so every two/three days over the space of a couple of weeks). It's possible that at the moment she only needs around the ten hours mark at night, so it may not be daylight per se that's wakening her.