VCO from a rectangular and triangular signal generator
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. A "get you going" modification.

Your circuit isn't voltage controlled but can be modified to give manual control. 


Addition of R7 varies the rate that C1 charges (the integral time) and hence the frequency. 
For single-ended supply you need to bias the op-amps to mid supply. This is done by R8 and R9 and an additional non-inverting, voltage follower, op-amp (OA3) here would help buffer the V+/2 voltage.
For 0 - 5 V triangle output with a 5 V supply you need op-amps with rail to rail outputs.
To attenuate the squarewave you can add a potential divider or pot, R6, from the output to mid-supply will suffice.