Very easy to change by yourself. From step two in the above mentioned link, I suggest you put it in exactly as pictured, but instead of pushing firmly, pry gently so the slim part of the metal key slides under the small piece of plastic that clips the cover in place. Use a flashlight to look into the hole and you'll see what I mean. Pushing in too hard may break the plactic off.
BTW, unless BMW has changed their policy, keyfob batteries can be changed at the dealer for free. I had two changes with my E60 but non yet with my F10. Once changed they are under warranty for two years (which is when they mysteriously wear out again).
2012 BMW 535i X-drive; Space Grey/Black Dakota, Fineline; Executive (Auto trunk, NAV, HiFi Prof, Lumbar, Rear Cam, SIRIUS, Voice), Technology (Blind Spot, Hi-Beam Assist, Lane Departure, Surround View), APPS, Rear heated seats, Tint.
Retired: 78 300D, 81 300SD, 87 190E, 88 Porsche 924, 89 260E, 93 300E, 97 Volvo 850, 98 E320, 03 BMW 325iT, 02 C230 Sport Coupe, 08 BMW 535i