There are two differ locations that you can change the Fundraising Goal for a TeamRaiser.  The location that you make the change depends on one of two things:

A) If you want the TeamRaiser to have a goal that is different from that specified in the associated Donation Campaign:
  1. Go to Fundraising -> TeamRaiser.
  2. Edit the TeamRaiser Event.
  3. Go to 2. Select Fundraising Options.
  4. Check "Yes, this TeamRaiser will have a goal that is different from any goals specified for the donation campaign."
  5. Enter the goal under 3. Fundraising Goal Amount.
  6. Click Save.

B) If you don't want the TeamRaiser goal to differ from the Donation Campaign:
  1. Go to Fundraising -> Donation Management.
  2. Find the Donation Campaign and click Edit.
  3. Go to 2. Choose Financial Options.
  4. Enter the goal under 2. Fundraising Goal.