Brake lever installation

Lever should be straight forward replacement, take time and look around, for example on a HD, there is a pin that holds the lever and a C shaped clip that holds the pin, you'll need the proper tool to remove the circle clip and that can be obtained at any parts store, Harbor Freight is cheap if you are on a tight budget find a Harbor Freight store to get your tools up to par.

On the Hd remove the clip, slide out the pin and the brake lever will come right out, I would bet your lever is not much different.

Be careful when removing and putting in the lever to not hurt any components such as a brake switch for tailight, you have to be observant of the steps

As to bad back brakes I don't buy it, they may not stop a Howsyabusha at 190 but you don't have a heavy big bike.

Check pads for wear, get a good set of aftermarket pads, replace them, and check the rotor if it looks good and make sure the caliper and rotor are in alignment.

Thenget some new DOT4 or DOT5 break fluid whatever the manual calls for, get a break bleeding kit from an Autozone, cheap, follow the instructions, change the fluid, (a syringe to remove old from the Master Cyl is good) Add new fluids and pump out the oil.

Bleeding brakes can be a PIA and a two person job so see if you can get someone to help, lotsa guys will help gals do this stuff or get a gal friend if you can read and turn a wrench you can do this.

Brakes are 80% front 20% rear on a bike.