I find the easiest way with the sword is to wiggle it left and right, so you kind of unlock one side first and then the other.
The two clips on the bottom of the tank should fit into the groove on his fore arm.

See the black lines on his left fore-arm, that is where the tank clips go over. Or the equivalent area on either arm... I have mine somewhere nearby at home, might get around to taking pics tonight if I remember. But for now, I hope this explains ok.
As for Soundwave tips, I find the wheels of the back of the van seem to get in the way a little bit when Transforming, so keep and eye on them and wigle them in/out of way as required. Half the time my one's arms pop off at the bicpe, but they easily go back in again so no dramas there. Legs can be a little fiddley, so just go slowly. they aren't THAT intuitive imo but the bonnet folds up and around to form the shins. Once again, I'll ahve a look when I get home, I can't remember what step 2 is...
His vehicle mode doesn't clip together very well either. Sad face.
Now you just need to find
Soundwave's official headband 