I would like display current against time instead of volts against time. Using Ohm's law I can calculate the current from the voltage but I was wondering if there is a way of changing the y-axis ?

Yes, by using Pico scope 2205 (using Pico scope 6 software), with the "custom probes" feature in PicoScope. Click the Channel Options button for the relevant channel, then click the button with three dots to the right of the word "Probe". This opens the Custom Probes dialog. Click "New Probe" and fill in the series of dialogs that appears. Ignore all the advanced options, choose "amperes" as the display unit and "linear equation" as the scaling method, and enter the desired conversion factor in the "gradient" box. Back in the Channel Options dialog, select the new probe that you have just created, and you will then see the vertical axis correctly scaled in milliamps.