It's requested through this link:
https://www.united.com/web/en-us/app...de.aspx?POS=US
Remember that *A upgrades using miles are only for instantly-confirmed upgrades. Upgrades that are not available cannot be waitlisted.
PS - personally I find 10,000 miles a waste on a short route like SIN-DPS. SQ has great service but 10,000 gets you a free ticket in the US under 700 miles. Obviously we all choose how to spend our miles differently.
-RM