If you want to change pitch using Audacity, this is basically:
- Mark the region you want to change the pitch of.
- Go to "Effect" --> "Change Pitch..."
- Pitch "from" on the left side should show the analyzed C3.
- Set "to" on the right side to D#4.
You can also set the frequency values instead. I recommend to use the "Use high quality stretching" option. Note that this function was not part of very early Audacity versions (I'm lacking version numbers here.)
Please have a look at the documentation in case of further questions.
The result will sound unnatural, because plain pitch-shifting your voice also changes your voice's formants. Hence, when the pitch is set to your desired target frequency, you have to lower the formants back to their original frequency region (downwards some 15 semitones again) to get a more natural formants sound. Please have a look at this discussion. You might have to experiment with the formant-pitch values to get best results.
In case you have access to a VST host / DAW or similar, you should maybe better try a professional plugin for changing pitch and formants (seperately), like maybe this one. Audacity also works with some VST plugins, but I do not have any experience in it.