Initially, its ok just to have higher reps mayb start at 8 (lower ur weights to 90% of current weight), it'll condition ur joints/tendons to carry heavier later. Work your way up to 12 reps, then up the weights.

It'll boost ur confidence & feel good factor when u can c weight improvements.

Anyhow, u have been into bb b4 right ? Then 4 reps shouldn't b much of a concern. Mayb u can rest bar for a few seconds, then con't to do 5th rep. Thats it , stop. After 2-3 workouts of this forced last rep, ur 5th rep shld come easily subsequently.

Good luck...