Don't!!!
Don't do it.
The HK USP line is very accurate and has nice big sights, but that's about it. I've owned a .45 USP fullsize and a .40 compact.
My .45 broke a firing pin during live fire. The rear half of the pin shot out the back, hitting me in the face. The front half of the pin wedged between the slide and the frame, taking a chunk out of the polymer frame about 1cm square.
The HK has an awful double action pull. LOTs of creep and just TERRIBLE stacking. They've improved it recently, but it really is p*ss-poor compared to the SIG.
The HK has a high bore axis and a lot of muzzle flip. The grip is unnecessarily wide for a 10-rounder.
My Sig 226 fits my hand like a glove and is the only handgun I've owned that has NEVER had a jam or FTF. The HKs are very accurate, but you can get it to stovepipe. Also the chamber is very generous, almost oversize, so if you reload your ammo, the cases soot really badly. Trust me, this gets old after 100 rounds or so. It also contributes to premature wear in the chamber.
Check the web and you'll see that prices on USPs are dropping, and there are a LOT for sale. Reason is they're OK, but nothing great. The tactical is just an overpriced long-slide version with the same fundamental flaws as the basic.
Keep your Sig, save your money. If you want an HK, buy a P7. Now that's a great pistol.