Instant Member does not include OTO (one time offer) integration as it is (commonly) used these days.  But it does provide you with the ability to offer limitless Upsells to each membership level you create (we believe this to be much more effective)

Using the 'Membership Upsells' option inside the admin panel in combination with the powerful 'member level content' feature you can upsell specific membership ugrades to each of your members.

For example:
Bronze Membership to Silver Memberships
Bronze Membershio direct to Gold Memberships
Bronze Memberships direct to Platinum Memberships

On each upsell you can set the price/payment gateway and commission level amounts (paid to the original referrer)

And you can create these upsells in any combination of:

Any One Time Fee Membership To Any Other One Time Fee Membership 
A Subscription Membership To Any Other Subscription Membership 
Free Membership Upsell To Any Membership Level