You'll need to replace the entire crankset.

Refer to this exploded diagram from techdocs.shimano.com and you'll see why.

While the left crankarm is a separate part and is easily replaceable, the right crankarm is not. It's a one-piece unit that also includes the spider that the chanirings bolt to, and the crankshaft itself, which goes through the bottom bracket and comes out the other side for the left crankarm to bolt to.

Any of Shimano's current "two-piece" or "Hollowtech II" road cranksets will work--from Sora all the way up to Dura-Ace--and most of the "non-group" cranksets like your R553. Claris group and below, and the non-group "Octalink" cranks, require a different bottom bracket than you have.

Alternatively, by changing the bottom bracket, you can use any crankset, even other brands.