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What do mean by "nice photos"?
I'd argue that a DSLR will not let you take nicer photos.
You'd getter more shallow depth of field, depending on the lens you use and high iso-performance might improve, but it will not make your photos any better, that's up to you.
I'd invest the money in a nice prime for your Olympus instead. Something like the 17mm or 25mm f1.8.But if you're hell bent on a DSLR a Nikon D3XXX with a 35mm f1.8 is great bit of kit.
Do you have any photografic experience?
If not, your pictures probably won't be any better on a DSLR - however, if it encourages you to take more pictures and practice then by all means go for it.
You really can't go wrong with anything from Canon or Nikon.