The ~50 second video above gives a quick walkthrough. You can send Updates to anyone in a fundraising stage by selecting the respective stage in the "to" field in your Update.
Here is how to get there:
Updates -> Send -> Click into "to"
Helpful Notes:
You'll have to have stages created in Fundraising.
At least one contact will have to be created/assigned in the investor record for the stage to show up and be selected in Update recipients.