You're riding on a time-bomb.
The solder (even if it's silver-soldered or brazed) isn't strong enough to last -- and could possibly fail dramatically in a panic stop. Fortunately, you've got a dual system, which crosses the left front with the right rear, and vice-versa.
Ok, you knew that you needed to change it or you wouldn't have asked.
The brake line is steel. You buy it in lengths close to your needs. If lucky, you can get one that's so close that you merely add a few clever (and properly radiused) bends to take up the slack.
Don't bend it by hand -- buy a cheap tubing bender.
If you need to cut, you need to 'double-flare' the end that you cut. Double-flaring is tricky -- needs a special tool -- and often splits unless the burrs are properly removed prior to the flaring process.
Not to worry, since once you've bent the tubing to 'close' (as in: but no cigar), you can take your work of art to the auto parts house where you can get a free tutorial on cussing and making a double-flare (be sure to put the damned fitting on before you flare it).
The hardest part is removing the old tubing and bending the new one (duhhh) -- but it's a satisfying experience.