General:
* I want to inform you.
* I'd like to let you know.
* I want to tell you.
Formal:
* I wish to inform you.
* I would like to bring to your attention.
Specific:
* I want to inform you about [topic].
* I want to let you know that [statement].
For example:
* "Gusto kong ipaalam na pupunta ako sa mall bukas." - I want to let you know that I'm going to the mall tomorrow.
* "Gusto kong ipaalam sa lahat na ang meeting ay kanselado." - I want to inform everyone that the meeting is canceled.
Choose the translation that best fits the context and your desired level of formality.