You should check this answer: https://quant.stackexchange.com/questions/30258/how-to-interpret-the-price-of-a-cds/30263#30263

It explains the relation between spread and upfront.
In your particular case you might consider using a simple model mentioned at the end of that answer:

> A simple model for the value of a short protection CDS can be found if you write
>
>V = (C-S) x RPV01
>
>where
>
>RPV01 = (1−exp(−gT))/g
>
>and C is the coupon, S is the par CDS spread, T is the remaining life in years and
>
>g=r+S/(1−R)g=r+S/(1−R)
>
>where r is the risk-free (Libor) rate and R is the expected recovery rate, usually set to 40%.