Differential amplifier with a current source
This is an AC amplifier, as C1 removes any dependence on the DC level at the input. Simply move the voltage at Q1 and Q2 bases up, by increasing R12 and R22. This will give you enough voltage headroom (tailroom?) for Q4 to operate down to ground. R1 now goes to ground, and Q4 base to a positive voltage.

In order to minimise the design changes, it would be useful to increase the V+ supply, and increase the other resistors to ground.

Note that if you'd used the built in schematic editor for presenting the circuit, rather than embedding it as an image, I could have copied it and edited it to show you exactly what I meant.