Pricing Plan Upgrade Option

I want to be able to get my customers to upgrade their plan to a higher paying one.

At the minute I have 3 plans. (Free | £100/month | £500/Month)

If they are on the £100/month plan and want to upgrade they currently have to buy the £500 plan and then cancel their existing £100 one. Is there a way to automatically cancel their £100 plan if they do this?