Where the land is lowest but level, you should probably leave undisturbed, and try to lower the higher section.
There are many ways to level, but probably the best involves using a transit and somebody holding a marked stick--even a good 1" wide tape measure can work.
Equally good is a laser level and you can use the laser with the marked stick so one person can do it.
But these tools are expensive.

For far less money you can use what's called "Mason's Line" and string levels. Mason's Line can be pulled taught as a guitar string and tied off, with the levels set at either end to show when the string(s) are level. Usually, you put the string ABOVE what you want level by the thickness of the 2x4, about 3 5/8". If you have a string on either side, using a straight long 2x4 you can find the high and low spots and even them off. Mason's Line comes in white, yellow, green, and, I kid you not, hot pink!

Carl