Megan. 

Thank  you for reaching out to the UNH Extension Infoline.

Rosa rugosa or beach roses are exceptionally hardy and will naturally rejuvenate from the base.

The best time to cut them close to the ground is now i.e. late winter, early spring.

I would suggest that you clear the area around the rose bush and remove any dead, damaged or diseased wood. Remove any crossing canes and central canes to promote air circulation. You will now be able to take the rest of the stems down to 6" - 12" above the ground, if possible leaving only 3-6 canes. I would note that the lower the cut the stronger the growth will be. 

 When you make the cuts, cut above a bud at a downward 45 degree angle, allowing rain water to run off.

Beach roses are one of the few varieties that respond beautifully to being cut nearly to the ground.

I trust this helps.