IAP 205H minimum Instant OS is 4.2.0.0
IAP-207 minimum InstantOS is 4.3.1.0.
IAP-303H minimum InstantOS is 6.5.2.0/8.2.0.0
IAP-203H minimum InstantOS is 6.5.3.0/8.2.0.0
So it means that you have to upgrade the existing iAPs to 4.3.1.0 and it shouldn't be a problem to support IAP-207.
On the regards of IAP-303H & IAP-203H, if you want to move to those IAPs, then you have to upgrade the existing IAP to 6.5.2.0 or 6.5.3.0.
The IAP-205H supports 6.5.3.0, check the image attached.
Refer to the Datasheets bellow as well for the InstantOS supported by IAPs:
IAP-207 https://www.arubanetworks.com/assets/ds/DS_AP207Series.pdf
IAP-205H https://www.arubanetworks.com/assets/ds/DS_AP205H.pdf
IAP-303H https://www.arubanetworks.com/assets/ds/DS_AP303H.pdf
IAP-203H https://www.arubanetworks.com/assets/ds/DS_AP203H.pdf